commit 22c63043e69d2c715c3bd1f772b5ec718f645823
Author: Madeorsk <madeorsk@protonmail.com>
Date:   Fri Nov 8 16:33:44 2024 +0100

    Initialize Nest databases library.

diff --git a/.gitignore b/.gitignore
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index 0000000..2dfd9ec
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,6 @@
+# IDEA
+.idea/
+*.iml
+
+# Composer
+vendor/
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..4fd0c62
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,60 @@
+{
+	"version": "dev-main",
+	"name": "nest/database",
+	"description": "Nest databases service.",
+	"type": "library",
+	"authors": [
+		{
+			"name": "Madeorsk",
+			"email": "madeorsk@protonmail.com"
+		}
+	],
+	"autoload": {
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+			"Nest\\Database\\": "src/"
+		},
+		"files": [
+			"src/Utils/Sql.php"
+		]
+	},
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+			"url": "https://code.zeptotech.net/Nest/Core"
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+            "name": "symfony/polyfill-uuid",
+            "version": "v1.31.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/polyfill-uuid.git",
+                "reference": "21533be36c24be3f4b1669c4725c7d1d2bab4ae2"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/polyfill-uuid/zipball/21533be36c24be3f4b1669c4725c7d1d2bab4ae2",
+                "reference": "21533be36c24be3f4b1669c4725c7d1d2bab4ae2",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=7.2"
+            },
+            "provide": {
+                "ext-uuid": "*"
+            },
+            "suggest": {
+                "ext-uuid": "For best performance"
+            },
+            "type": "library",
+            "extra": {
+                "thanks": {
+                    "name": "symfony/polyfill",
+                    "url": "https://github.com/symfony/polyfill"
+                }
+            },
+            "autoload": {
+                "files": [
+                    "bootstrap.php"
+                ],
+                "psr-4": {
+                    "Symfony\\Polyfill\\Uuid\\": ""
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Grégoire Pineau",
+                    "email": "lyrixx@lyrixx.info"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Symfony polyfill for uuid functions",
+            "homepage": "https://symfony.com",
+            "keywords": [
+                "compatibility",
+                "polyfill",
+                "portable",
+                "uuid"
+            ],
+            "support": {
+                "source": "https://github.com/symfony/polyfill-uuid/tree/v1.31.0"
+            },
+            "funding": [
+                {
+                    "url": "https://symfony.com/sponsor",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/fabpot",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2024-09-09T11:45:10+00:00"
+        },
+        {
+            "name": "symfony/translation",
+            "version": "v7.1.6",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/translation.git",
+                "reference": "b9f72ab14efdb6b772f85041fa12f820dee8d55f"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/translation/zipball/b9f72ab14efdb6b772f85041fa12f820dee8d55f",
+                "reference": "b9f72ab14efdb6b772f85041fa12f820dee8d55f",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=8.2",
+                "symfony/polyfill-mbstring": "~1.0",
+                "symfony/translation-contracts": "^2.5|^3.0"
+            },
+            "conflict": {
+                "symfony/config": "<6.4",
+                "symfony/console": "<6.4",
+                "symfony/dependency-injection": "<6.4",
+                "symfony/http-client-contracts": "<2.5",
+                "symfony/http-kernel": "<6.4",
+                "symfony/service-contracts": "<2.5",
+                "symfony/twig-bundle": "<6.4",
+                "symfony/yaml": "<6.4"
+            },
+            "provide": {
+                "symfony/translation-implementation": "2.3|3.0"
+            },
+            "require-dev": {
+                "nikic/php-parser": "^4.18|^5.0",
+                "psr/log": "^1|^2|^3",
+                "symfony/config": "^6.4|^7.0",
+                "symfony/console": "^6.4|^7.0",
+                "symfony/dependency-injection": "^6.4|^7.0",
+                "symfony/finder": "^6.4|^7.0",
+                "symfony/http-client-contracts": "^2.5|^3.0",
+                "symfony/http-kernel": "^6.4|^7.0",
+                "symfony/intl": "^6.4|^7.0",
+                "symfony/polyfill-intl-icu": "^1.21",
+                "symfony/routing": "^6.4|^7.0",
+                "symfony/service-contracts": "^2.5|^3",
+                "symfony/yaml": "^6.4|^7.0"
+            },
+            "type": "library",
+            "autoload": {
+                "files": [
+                    "Resources/functions.php"
+                ],
+                "psr-4": {
+                    "Symfony\\Component\\Translation\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Fabien Potencier",
+                    "email": "fabien@symfony.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Provides tools to internationalize your application",
+            "homepage": "https://symfony.com",
+            "support": {
+                "source": "https://github.com/symfony/translation/tree/v7.1.6"
+            },
+            "funding": [
+                {
+                    "url": "https://symfony.com/sponsor",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/fabpot",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2024-09-28T12:35:13+00:00"
+        },
+        {
+            "name": "symfony/translation-contracts",
+            "version": "v3.5.0",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/translation-contracts.git",
+                "reference": "b9d2189887bb6b2e0367a9fc7136c5239ab9b05a"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/translation-contracts/zipball/b9d2189887bb6b2e0367a9fc7136c5239ab9b05a",
+                "reference": "b9d2189887bb6b2e0367a9fc7136c5239ab9b05a",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=8.1"
+            },
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-main": "3.5-dev"
+                },
+                "thanks": {
+                    "name": "symfony/contracts",
+                    "url": "https://github.com/symfony/contracts"
+                }
+            },
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Contracts\\Translation\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Test/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Nicolas Grekas",
+                    "email": "p@tchwork.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Generic abstractions related to translation",
+            "homepage": "https://symfony.com",
+            "keywords": [
+                "abstractions",
+                "contracts",
+                "decoupling",
+                "interfaces",
+                "interoperability",
+                "standards"
+            ],
+            "support": {
+                "source": "https://github.com/symfony/translation-contracts/tree/v3.5.0"
+            },
+            "funding": [
+                {
+                    "url": "https://symfony.com/sponsor",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/fabpot",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2024-04-18T09:32:20+00:00"
+        },
+        {
+            "name": "symfony/uid",
+            "version": "v7.1.6",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/symfony/uid.git",
+                "reference": "65befb3bb2d503bbffbd08c815aa38b472999917"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/symfony/uid/zipball/65befb3bb2d503bbffbd08c815aa38b472999917",
+                "reference": "65befb3bb2d503bbffbd08c815aa38b472999917",
+                "shasum": ""
+            },
+            "require": {
+                "php": ">=8.2",
+                "symfony/polyfill-uuid": "^1.15"
+            },
+            "require-dev": {
+                "symfony/console": "^6.4|^7.0"
+            },
+            "type": "library",
+            "autoload": {
+                "psr-4": {
+                    "Symfony\\Component\\Uid\\": ""
+                },
+                "exclude-from-classmap": [
+                    "/Tests/"
+                ]
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "MIT"
+            ],
+            "authors": [
+                {
+                    "name": "Grégoire Pineau",
+                    "email": "lyrixx@lyrixx.info"
+                },
+                {
+                    "name": "Nicolas Grekas",
+                    "email": "p@tchwork.com"
+                },
+                {
+                    "name": "Symfony Community",
+                    "homepage": "https://symfony.com/contributors"
+                }
+            ],
+            "description": "Provides an object-oriented API to generate and represent UIDs",
+            "homepage": "https://symfony.com",
+            "keywords": [
+                "UID",
+                "ulid",
+                "uuid"
+            ],
+            "support": {
+                "source": "https://github.com/symfony/uid/tree/v7.1.6"
+            },
+            "funding": [
+                {
+                    "url": "https://symfony.com/sponsor",
+                    "type": "custom"
+                },
+                {
+                    "url": "https://github.com/fabpot",
+                    "type": "github"
+                },
+                {
+                    "url": "https://tidelift.com/funding/github/packagist/symfony/symfony",
+                    "type": "tidelift"
+                }
+            ],
+            "time": "2024-09-25T14:20:29+00:00"
+        }
+    ],
+    "packages-dev": [],
+    "aliases": [],
+    "minimum-stability": "stable",
+    "stability-flags": {
+        "nest/cli": 20,
+        "nest/core": 20,
+        "nest/events": 20,
+        "nest/model": 20,
+        "nest/types": 20
+    },
+    "prefer-stable": false,
+    "prefer-lowest": false,
+    "platform": {
+        "php": "^8.3",
+        "ext-pdo": "*"
+    },
+    "platform-dev": {},
+    "plugin-api-version": "2.6.0"
+}
diff --git a/src/Cli/Migrations/MigrateCommand.php b/src/Cli/Migrations/MigrateCommand.php
new file mode 100644
index 0000000..57fa19f
--- /dev/null
+++ b/src/Cli/Migrations/MigrateCommand.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Nest\Database\Cli\Migrations;
+
+use Nest\Application;
+use Nest\Cli\Commands\CommandHandler;
+use Nest\Cli\Out;
+use Nest\Database\Migrations\Migration;
+use Nest\Database\Exceptions\Migrations\MigrationNotFoundException;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+use Nest\Database\Exceptions\UnknownDatabaseException;
+use Nest\Model\Exceptions\MissingRequiredFieldException;
+use Nest\Types\Exceptions\IncompatibleTypeException;
+use Throwable;
+
+class MigrateCommand extends CommandHandler
+{
+	/**
+	 * @throws Throwable
+	 * @throws MigrationNotFoundException
+	 * @throws IncompatibleTypeException
+	 * @throws UnknownDatabaseException
+	 * @throws MissingConditionValueException
+	 * @throws MissingRequiredFieldException
+	 */
+	public function __invoke(): void
+	{
+		Application::get()->migrations()->onMigrationStart = function (Migration $migration) {
+			Out::print("Executing migration V{$migration->getVersion()} ".Out::BOLD_ATTRIBUTE."{$migration->getName()}".Out::RESET_ATTRIBUTES);
+			echo "  ".Out::ITALIC_ATTRIBUTE.$migration->getDescription().Out::RESET_ATTRIBUTES."\n\n";
+		};
+		Application::get()->migrations()->onMigrationEnd = function (Migration $migration) {
+			echo "\n";
+			Out::print("V{$migration->getVersion()}_{$migration->getName()} finished.");
+			echo "\n";
+		};
+
+		// Execute all remaining migrations.
+		Application::get()->migrations()->load()->migrate();
+
+		Out::success("Migrations executed successfully.");
+	}
+}
diff --git a/src/Cli/Migrations/MigrateOneCommand.php b/src/Cli/Migrations/MigrateOneCommand.php
new file mode 100644
index 0000000..0399d2b
--- /dev/null
+++ b/src/Cli/Migrations/MigrateOneCommand.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Nest\Database\Cli\Migrations;
+
+use Nest\Application;
+use Nest\Cli\Commands\CommandHandler;
+use Nest\Cli\Out;
+use Nest\Database\Migrations\Migration;
+use Nest\Database\Exceptions\Migrations\MigrationNotFoundException;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+use Nest\Database\Exceptions\UnknownDatabaseException;
+use Nest\Model\Exceptions\MissingRequiredFieldException;
+use Nest\Types\Exceptions\IncompatibleTypeException;
+use Throwable;
+
+class MigrateOneCommand extends CommandHandler
+{
+	/**
+	 * @throws Throwable
+	 * @throws MigrationNotFoundException
+	 * @throws IncompatibleTypeException
+	 * @throws UnknownDatabaseException
+	 * @throws MissingConditionValueException
+	 * @throws MissingRequiredFieldException
+	 */
+	public function __invoke(string $migrationId): void
+	{
+		Application::get()->migrations()->onMigrationStart = function (Migration $migration) {
+			Out::print("Executing migration V{$migration->getVersion()} ".Out::BOLD_ATTRIBUTE."{$migration->getName()}".Out::RESET_ATTRIBUTES);
+			echo "  ".Out::ITALIC_ATTRIBUTE.$migration->getDescription().Out::RESET_ATTRIBUTES."\n\n";
+		};
+		Application::get()->migrations()->onMigrationEnd = function (Migration $migration) {
+			echo "\n";
+			Out::print("V{$migration->getVersion()}_{$migration->getName()} finished.");
+			echo "\n";
+		};
+
+		// Try to execute given migration.
+		Application::get()->migrations()->load()->migrateOne($migrationId);
+
+		Out::success("Success.");
+	}
+}
diff --git a/src/Cli/Migrations/MigrationsCommands.php b/src/Cli/Migrations/MigrationsCommands.php
new file mode 100644
index 0000000..92986db
--- /dev/null
+++ b/src/Cli/Migrations/MigrationsCommands.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Nest\Database\Cli\Migrations;
+
+use Nest\Cli\Cli;
+use Nest\Cli\Commands\CommandDefinition;
+use Nest\Cli\Commands\ParameterDefinition;
+use Nest\Cli\Exceptions\Command\InvalidCommandHandlerException;
+use Nest\Cli\Exceptions\IncompatibleCliHandlerSubcommands;
+
+/**
+ * Migrations commands definition manager.
+ */
+class MigrationsCommands
+{
+	/**
+	 * @param Cli $cli The CLI in which to define migrations commands.
+	 * @return void
+	 * @throws IncompatibleCliHandlerSubcommands
+	 * @throws InvalidCommandHandlerException
+	 */
+	public static function define(Cli $cli): void
+	{
+		$cli->command("migrations")
+			->description("Migrations manager.")
+			->subcommands([
+				"migrate" => fn (CommandDefinition $subcommand) => $subcommand
+					->description("Execute all remaining migrations.")
+					->handler(MigrateCommand::class)
+				,
+				"migrateOne" => fn (CommandDefinition $subcommand) => $subcommand
+					->description("Perform one migration.")
+					->parameter("migrationId", fn (ParameterDefinition $parameter) => $parameter->description("Migration ID of migration to execute."))
+					->handler(MigrateOneCommand::class)
+				,
+				"rollback" => fn (CommandDefinition $subcommand) => $subcommand
+					->description("Rollback latest migration.")
+					->handler(RollbackCommand::class)
+				,
+				"new" => fn (CommandDefinition $subcommand) => $subcommand
+					->description("Generate a migration with the given name.")
+					->parameter("name", fn (ParameterDefinition $parameter) => $parameter->description("Name of the new migration."))
+					->handler(NewCommand::class)
+				,
+			]);
+	}
+}
diff --git a/src/Cli/Migrations/NewCommand.php b/src/Cli/Migrations/NewCommand.php
new file mode 100644
index 0000000..52ba86e
--- /dev/null
+++ b/src/Cli/Migrations/NewCommand.php
@@ -0,0 +1,18 @@
+<?php
+
+namespace Nest\Database\Cli\Migrations;
+
+use Nest\Application;
+use Nest\Cli\Commands\CommandHandler;
+use Nest\Cli\Out;
+
+class NewCommand extends CommandHandler
+{
+	public function __invoke(string $name): void
+	{
+		// Create a new migration.
+		Application::get()->migrations()->newMigration($name);
+
+		Out::success("Migration successfully created.");
+	}
+}
diff --git a/src/Cli/Migrations/RollbackCommand.php b/src/Cli/Migrations/RollbackCommand.php
new file mode 100644
index 0000000..20e7cc0
--- /dev/null
+++ b/src/Cli/Migrations/RollbackCommand.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace Nest\Database\Cli\Migrations;
+
+use Nest\Application;
+use Nest\Cli\Commands\CommandHandler;
+use Nest\Cli\Out;
+use Nest\Database\Migrations\Migration;
+use Nest\Database\Exceptions\Migrations\MigrationNotFoundException;
+use Throwable;
+
+class RollbackCommand extends CommandHandler
+{
+	/**
+	 * @throws MigrationNotFoundException
+	 * @throws Throwable
+	 */
+	public function __invoke(): void
+	{
+		Application::get()->migrations()->onRollbackStart = function (Migration $migration) {
+			Out::print("Starting to roll back V{$migration->getVersion()} ".Out::BOLD_ATTRIBUTE."{$migration->getName()}".Out::RESET_ATTRIBUTES);
+			echo "  ".Out::ITALIC_ATTRIBUTE.$migration->getDescription().Out::RESET_ATTRIBUTES."\n\n";
+		};
+
+		// Rollback latest migration.
+		$migration = Application::get()->migrations()->load()->rollbackLatest();
+
+		if (!empty($migration))
+			Out::success("Rolled back V{$migration->getVersion()} {$migration->getName()}");
+		else
+			Out::warning("Nothing to rollback.");
+	}
+}
diff --git a/src/Configuration/DatabaseFactory.php b/src/Configuration/DatabaseFactory.php
new file mode 100644
index 0000000..5e9d7e0
--- /dev/null
+++ b/src/Configuration/DatabaseFactory.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace Nest\Database\Configuration;
+
+use Nest\Database\Database;
+use Nest\Database\Exceptions\Configuration\MissingRequiredConfigurationValueException;
+
+/**
+ * Create a database object from a configuration array.
+ */
+abstract class DatabaseFactory
+{
+	/**
+	 * @param string $databaseIdentifier Database identifier.
+	 * @param array $configuration Database configuration array.
+	 */
+	public function __construct(protected string $databaseIdentifier, protected array $configuration)
+	{}
+
+	/**
+	 * Get a required configuration value.
+	 * @param string $configKey Configuration key.
+	 * @return mixed Configuration value.
+	 * @throws MissingRequiredConfigurationValueException
+	 */
+	public function getRequiredConfig(string $configKey): mixed
+	{
+		if (!isset($this->configuration[$configKey]))
+			throw new MissingRequiredConfigurationValueException($this->databaseIdentifier, static::class, $configKey);
+
+		return $this->configuration[$configKey];
+	}
+
+	/**
+	 * Get an optional configuration value.
+	 * @param string $configKey Configuration key.
+	 * @param mixed|null $default Default configuration value.
+	 * @return mixed Configuration value.
+	 */
+	public function getOptionalConfig(string $configKey, mixed $default = null): mixed
+	{
+		return $this->configuration[$configKey] ?? $default;
+	}
+
+	/**
+	 * Make the database object from its configuration array.
+	 * @return Database The created database.
+	 * @throws MissingRequiredConfigurationValueException
+	 */
+	public abstract function make(): Database;
+}
diff --git a/src/Configuration/DatabasesArrayConfiguration.php b/src/Configuration/DatabasesArrayConfiguration.php
new file mode 100644
index 0000000..0fda6fd
--- /dev/null
+++ b/src/Configuration/DatabasesArrayConfiguration.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Nest\Database\Configuration;
+
+use Nest\Application;
+use Nest\Configuration\Exceptions\ConfigurationValueNotFoundException;
+use Nest\Database\Exceptions\Configuration\UndefinedDatabaseTypeException;
+
+class DatabasesArrayConfiguration extends DatabasesConfiguration
+{
+	/**
+	 * @param Application $application The application.
+	 * @param string $configurationKey Configuration key where to find the databases configuration array.
+	 */
+	public function __construct(protected Application $application, protected string $configurationKey)
+	{}
+
+	/**
+	 * @inheritDoc
+	 * @throws ConfigurationValueNotFoundException
+	 * @throws UndefinedDatabaseTypeException
+	 */
+	#[\Override] public function getFactories(): array
+	{
+		// Initialize loaded factories.
+		$factories = [];
+
+		foreach ($this->application->configuration()->getValue($this->configurationKey) as $identifier => $configuration)
+		{
+			if (empty($configuration["type"]))
+				// Undefined database type, throwing an exception.
+				throw new UndefinedDatabaseTypeException($identifier);
+
+			// Create the factory with the given configuration.
+			$factories[$identifier] = new $configuration["type"]($identifier, $configuration);
+		}
+
+		return $factories; // Return loaded factories.
+	}
+}
diff --git a/src/Configuration/DatabasesConfiguration.php b/src/Configuration/DatabasesConfiguration.php
new file mode 100644
index 0000000..88bc8f0
--- /dev/null
+++ b/src/Configuration/DatabasesConfiguration.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Nest\Database\Configuration;
+
+use Nest\Services\ServiceConfiguration;
+
+abstract class DatabasesConfiguration extends ServiceConfiguration
+{
+	/**
+	 * Get database factories.
+	 * @return array<string, DatabaseFactory> Database factories, indexed by databases identifiers.
+	 */
+	public abstract function getFactories(): array;
+}
diff --git a/src/Database.php b/src/Database.php
new file mode 100644
index 0000000..2059cb5
--- /dev/null
+++ b/src/Database.php
@@ -0,0 +1,144 @@
+<?php
+
+namespace Nest\Database;
+
+use Nest\Database\Query\QueryBuilder;
+use Nest\Database\Transactions\Transaction;
+use Nest\Database\Exceptions\NotCurrentTransactionException;
+use Throwable;
+
+/**
+ * Class of a database.
+ */
+abstract class Database
+{
+	/**
+	 * The current transaction, in one is started.
+	 * @var Transaction|null
+	 */
+	private ?Transaction $transaction = null;
+
+	/**
+	 * Connect to the database.
+	 * @return void
+	 */
+	public abstract function connect(): void;
+
+	/**
+	 * Execute a query.
+	 * @param string $statement The query statement.
+	 * @param array $bindings The query bindings.
+	 * @return object[] Query result as an array of objects.
+	 */
+	public abstract function execute(string $statement, array $bindings = []): array;
+
+	/**
+	 * Get a queries adapter for the current database.
+	 * @return DatabaseAdapter A database queries adapter.
+	 */
+	public abstract function getQueriesAdapter(): DatabaseAdapter;
+
+	/**
+	 * Create a new query on the database.
+	 * @param ?string $table The table on which to build the new query.
+	 * @return QueryBuilder A query builder.
+	 */
+	public function query(?string $table = null): QueryBuilder
+	{
+		return new QueryBuilder($this, $table);
+	}
+
+	/**
+	 * Create a new query on the given table of the database.
+	 * @param string $table The table on which to build the new query.
+	 * @return QueryBuilder A query builder.
+	 */
+	public function table(string $table): QueryBuilder
+	{
+		return $this->query($table);
+	}
+
+
+	/**
+	 * Get the current transaction, if there is one.
+	 * @return Transaction|null
+	 */
+	public function getCurrentTransaction(): ?Transaction
+	{
+		return $this->transaction;
+	}
+
+	/**
+	 * Called when the state of a transaction changed (inactive -> active or active -> inactive).
+	 * @param Transaction $transaction
+	 * @return void
+	 * @throws NotCurrentTransactionException
+	 */
+	public function onTransactionStateChanged(Transaction $transaction): void
+	{
+		if ($transaction->isActive())
+		{ // Set the newly active transaction as the current one.
+
+			// Its parent should be the current transaction, if it exists.
+			if (!empty($transaction->getParent()) && $transaction->getParent()->getUuid() != $this->transaction->getUuid())
+				throw new NotCurrentTransactionException($this->transaction, $transaction->getParent());
+
+			$this->transaction = $transaction;
+		}
+		else
+		{ // The transaction has been terminated, it should be the current one.
+			if (!empty($this->transaction) && $this->transaction->getUuid() != $transaction->getUuid())
+				throw new NotCurrentTransactionException($this->transaction, $transaction);
+
+			$this->transaction = $transaction->getParent();
+		}
+	}
+
+	/**
+	 * Start a new transaction (in the current one, if there is one).
+	 * @return Transaction The new transaction.
+	 * @throws NotCurrentTransactionException
+	 */
+	public function startTransaction(): Transaction
+	{
+		// Create the transaction as a child of the existing one, if there is one.
+		$newTransaction = new Transaction($this, $this->transaction);
+		if (!empty($this->transaction))
+			// Set the new transaction as child of the current one.
+			$this->transaction->setChild($newTransaction);
+
+		$newTransaction->start(); // Start the new transaction.
+
+		return $newTransaction; // Return the new transaction.
+	}
+
+	/**
+	 * Start a new transaction and execute the function in parameter.
+	 * The transaction will be committed / rolled back automatically at the end of the function.
+	 * A rollback happen if any exception is thrown in the function.
+	 * @param callable(Transaction): mixed $function The function to execute in a transaction.
+	 * @return mixed Function result.
+	 * @throws Throwable
+	 */
+	public function transaction(callable $function): mixed
+	{
+		// Start a new transaction.
+		$transaction = $this->startTransaction();
+
+		try
+		{ // Trying to run the function in the started transaction.
+			$result = $function($transaction);
+
+			// The function finished successfully, commit the transaction.
+			$transaction->commit();
+
+			// Return result of the function.
+			return $result;
+		}
+		catch (Throwable $throwable)
+		{ // An exception has been thrown, rolling back the transaction and throw it again.
+			$transaction->rollback();
+			throw $throwable;
+		}
+	}
+}
diff --git a/src/DatabaseAdapter.php b/src/DatabaseAdapter.php
new file mode 100644
index 0000000..dcef0cf
--- /dev/null
+++ b/src/DatabaseAdapter.php
@@ -0,0 +1,199 @@
+<?php
+
+namespace Nest\Database;
+
+use Nest\Database\Migrations\Diff\TableColumn;
+use Nest\Database\Migrations\Diff\TableForeignKey;
+use Nest\Database\Migrations\Diff\TableIndex;
+use Nest\Database\Query\Join\JoinBuilder;
+use Nest\Database\Query\Raw;
+use Nest\Database\Query\Where\ConditionBuilder;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+
+/**
+ * A database queries adapter.
+ */
+abstract class DatabaseAdapter
+{
+	/**
+	 * @param Database $database The database on which to execute the queries.
+	 */
+	public function __construct(protected Database $database)
+	{}
+
+	/**
+	 * Start a new transaction.
+	 * @return void
+	 */
+	public abstract function newTransaction(): void;
+
+	/**
+	 * Rollback the current transaction.
+	 * @return void
+	 */
+	public abstract function rollbackTransaction(): void;
+
+	/**
+	 * Commit the current transaction.
+	 * @return void
+	 */
+	public abstract function commitTransaction(): void;
+
+	/**
+	 * Perform a table creation.
+	 * @param string $tableName Name of the table to create.
+	 * @param bool $ifNotExists True to try to add if table does not exist, will just pass if it exists.
+	 * @return void
+	 */
+	public abstract function createTable(string $tableName, bool $ifNotExists = false): void;
+
+	/**
+	 * Perform a table deletion.
+	 * @param string $tableName Name of the table to drop.
+	 * @param bool $ifExists True to try to drop if table exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public abstract function dropTable(string $tableName, bool $ifExists = false): void;
+
+	/**
+	 * Rename a table.
+	 * @param string $tableName Table to rename.
+	 * @param string $newTableName New table name.
+	 * @return void
+	 */
+	public abstract function renameTable(string $tableName, string $newTableName): void;
+
+	/**
+	 * Add a column to a table.
+	 * @param TableColumn $tableColumn The column to add to a table.
+	 * @param bool $ifNotExists True to try to add if column does not exist, will just pass if it exists.
+	 * @return void
+	 */
+	public abstract function addTableColumn(TableColumn $tableColumn, bool $ifNotExists = false): void;
+
+	/**
+	 * Set index of a table column.
+	 * @param TableColumn $tableColumn The table column with index data.
+	 * @return void
+	 */
+	public abstract function setTableColumnIndex(TableColumn $tableColumn): void;
+
+	/**
+	 * Rename a table column.
+	 * @param TableColumn $tableColumn The table column to rename.
+	 * @param string $newName New name of the column.
+	 * @return void
+	 */
+	public abstract function renameTableColumn(TableColumn $tableColumn, string $newName): void;
+
+	/**
+	 * Modify a table colum.
+	 * @param TableColumn $tableColumn The column to modify.
+	 * @return void
+	 */
+	public abstract function alterTableColumn(TableColumn $tableColumn): void;
+
+	/**
+	 * Drop a table column.
+	 * @param string $tableName The table on which to drop a column.
+	 * @param string $columnName The column name to drop.
+	 * @param bool $ifExists True to try to drop if column exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public abstract function dropTableColumn(string $tableName, string $columnName, bool $ifExists = false): void;
+
+	/**
+	 * Drop a table constraint.
+	 * @param string $tableName The table on which to drop a constraint.
+	 * @param string $constraintName The constraint name to drop.
+	 * @param bool $ifExists True to try to drop if constraint exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public abstract function dropConstraint(string $tableName, string $constraintName, bool $ifExists = false): void;
+
+	/**
+	 * Create a foreign key constraint.
+	 * @param TableForeignKey $foreignKey The table foreign key to create.
+	 * @return void
+	 */
+	public abstract function createForeignKey(TableForeignKey $foreignKey): void;
+
+	/**
+	 * Create a table index.
+	 * @param TableIndex $index The table index to create.
+	 * @param bool $ifNotExists True to try to add if index does not exist, will just pass if it exists.
+	 * @return void
+	 */
+	public abstract function createIndex(TableIndex $index, bool $ifNotExists = false): void;
+
+	/**
+	 * Rename an existing index.
+	 * @param string $indexName The table index to rename.
+	 * @param string $newName The new name of the index.
+	 * @param bool $ifExists True to try to rename if index exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public abstract function renameIndex(string $indexName, string $newName, bool $ifExists = false): void;
+
+	/**
+	 * Drop a table index.
+	 * @param TableIndex $index The table index to drop.
+	 * @param bool $ifExists True to try to drop if index exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public abstract function dropIndex(TableIndex $index, bool $ifExists = false): void;
+
+	/**
+	 * Build a SELECT query.
+	 * @param string $tableName The table from which to select.
+	 * @param (Raw|string)[] $selected Selected columns from the table.
+	 * @param JoinBuilder[] $joins Joins of the query.
+	 * @param ConditionBuilder[] $wheres Conditions applied to rows for selection.
+	 * @param int|null $limit Limit of retrieved results. NULL by default = no limit.
+	 * @return Raw SQL and its bindings.
+	 * @throws MissingConditionValueException
+	 */
+	public abstract function buildSelect(string $tableName, array $selected, array $joins, array $wheres, ?int $limit = null): Raw;
+
+	/**
+	 * Select rows from a table.
+	 * @param string $tableName The table from which to select.
+	 * @param (Raw|string)[] $selected Selected columns from the table.
+	 * @param JoinBuilder[] $joins Joins of the query.
+	 * @param ConditionBuilder[] $wheres Conditions applied to rows for selection.
+	 * @param int|null $limit Limit of retrieved results. NULL by default = no limit.
+	 * @return object[] Selected rows objects.
+	 * @throws MissingConditionValueException
+	 */
+	public abstract function select(string $tableName, array $selected, array $joins, array $wheres, ?int $limit = null): array;
+
+	/**
+	 * Insert new rows in a table.
+	 * @param string $tableName The table where to insert.
+	 * @param string[] $columns Columns of the table that are provided in rows values.
+	 * @param array<string, Raw|string|int|float|null> $rows Rows values.
+	 * @param bool $returning True to return inserted objects.
+	 * @return object[]|bool Inserted rows objects if returning is true, true otherwise.
+	 */
+	public abstract function insert(string $tableName, array $columns, array $rows, bool $returning = false): array|bool;
+
+	/**
+	 * Update rows of a table.
+	 * @param string $tableName The table to update.
+	 * @param array<string, Raw|string|int|float|null> $set Set values in the rows.
+	 * @param ConditionBuilder[] $wheres Conditions applied to rows for update.
+	 * @param bool $returning True to return updated objects.
+	 * @return object[]|bool Updated rows objects if returning is true, true otherwise.
+	 * @throws MissingConditionValueException
+	 */
+	public abstract function update(string $tableName, array $set, array $wheres, bool $returning = false): array|bool;
+
+	/**
+	 * Delete rows from a table.
+	 * @param string $tableName The table in which to delete rows.
+	 * @param array $wheres Conditions applied to rows for deletion.
+	 * @return void
+	 * @throws MissingConditionValueException
+	 */
+	public abstract function delete(string $tableName, array $wheres): void;
+}
diff --git a/src/Databases.php b/src/Databases.php
new file mode 100644
index 0000000..d861c64
--- /dev/null
+++ b/src/Databases.php
@@ -0,0 +1,57 @@
+<?php
+
+namespace Nest\Database;
+
+use Nest\Application;
+use Nest\Database\Configuration\DatabasesConfiguration;
+use Nest\Database\Exceptions\Configuration\MissingRequiredConfigurationValueException;
+use Nest\Database\Exceptions\UnknownDatabaseException;
+
+/**
+ * Databases manager.
+ */
+class Databases
+{
+	/**
+	 * Loaded databases.
+	 * @var array<string, Database>
+	 */
+	private array $databases;
+
+	/**
+	 * @param Application $application Application of the databases.
+	 * @param DatabasesConfiguration $configuration Configuration of the databases.
+	 * @throws MissingRequiredConfigurationValueException
+	 */
+	public function __construct(protected Application $application, protected DatabasesConfiguration $configuration)
+	{
+		$this->load();
+	}
+
+	/**
+	 * Load databases from their factories.
+	 * @return void
+	 * @throws MissingRequiredConfigurationValueException
+	 */
+	public function load(): void
+	{
+		foreach ($this->configuration->getFactories() as $identifier => $databaseFactory)
+		{ // Load all databases from their factories.
+			$this->databases[$identifier] = $databaseFactory->make();
+		}
+	}
+
+	/**
+	 * @param string $identifier Database identifier.
+	 * @return Database Database corresponding to the given identifier.
+	 * @throws UnknownDatabaseException
+	 */
+	public function db(string $identifier): Database
+	{
+		if (empty($this->databases[$identifier]))
+			// Cannot find a database with this identifier, throwing an exception.
+			throw new UnknownDatabaseException($identifier);
+
+		return $this->databases[$identifier]; // Return loaded database.
+	}
+}
diff --git a/src/DatabasesService.php b/src/DatabasesService.php
new file mode 100644
index 0000000..6633e81
--- /dev/null
+++ b/src/DatabasesService.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace Nest\Database;
+
+use Nest\Database\Configuration\DatabasesConfiguration;
+use Nest\Database\Exceptions\Configuration\MissingRequiredConfigurationValueException;
+use Nest\Exceptions\Services\Configuration\UndefinedServiceConfigurationException;
+
+/**
+ * Databases Nest service.
+ */
+trait DatabasesService
+{
+	/**
+	 * The databases manager.
+	 * @var Databases
+	 */
+	private Databases $databases;
+
+	/**
+	 * @return void
+	 * @throws MissingRequiredConfigurationValueException
+	 * @throws UndefinedServiceConfigurationException
+	 */
+	protected function __nest__DatabasesService(): void
+	{
+		// Initialize databases manager.
+		$this->databases = new Databases($this, $this->getServiceConfiguration(DatabasesConfiguration::class));
+	}
+
+	/**
+	 * Databases service.
+	 * @return Databases The databases manager.
+	 */
+	public function databases(): Databases
+	{
+		return $this->databases;
+	}
+}
diff --git a/src/Events/PdoDatabaseAfterConnectionEvent.php b/src/Events/PdoDatabaseAfterConnectionEvent.php
new file mode 100644
index 0000000..4c13483
--- /dev/null
+++ b/src/Events/PdoDatabaseAfterConnectionEvent.php
@@ -0,0 +1,13 @@
+<?php
+
+namespace Nest\Database\Events;
+
+use Nest\Database\PdoDatabase;
+use Nest\Events\Event;
+use PDO;
+
+class PdoDatabaseAfterConnectionEvent extends Event
+{
+	public function __construct(public PdoDatabase $database, public PDO $pdo)
+	{}
+}
diff --git a/src/Events/PdoDatabaseBeforeConnectionEvent.php b/src/Events/PdoDatabaseBeforeConnectionEvent.php
new file mode 100644
index 0000000..64054aa
--- /dev/null
+++ b/src/Events/PdoDatabaseBeforeConnectionEvent.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Nest\Database\Events;
+
+use Nest\Database\PdoDatabase;
+use Nest\Events\Event;
+
+class PdoDatabaseBeforeConnectionEvent extends Event
+{
+	public function __construct(public PdoDatabase $database)
+	{}
+}
diff --git a/src/Exceptions/Configuration/MissingRequiredConfigurationValueException.php b/src/Exceptions/Configuration/MissingRequiredConfigurationValueException.php
new file mode 100644
index 0000000..f1ee596
--- /dev/null
+++ b/src/Exceptions/Configuration/MissingRequiredConfigurationValueException.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace Nest\Database\Exceptions\Configuration;
+
+use Nest\Database\Exceptions\DatabaseException;
+use Throwable;
+
+/**
+ * Thrown when database loading fails because of a missing required configuration.
+ */
+class MissingRequiredConfigurationValueException extends DatabaseException
+{
+	/**
+	 * @param string $databaseIdentifier Database identifier.
+	 * @param string $factoryClass Database factory class.
+	 * @param string $configKey Missing configuration key.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $databaseIdentifier, public string $factoryClass, public string $configKey, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Cannot load database $this->databaseIdentifier: cannot find required configuration $this->configKey for factory $this->factoryClass.", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/Configuration/UndefinedDatabaseTypeException.php b/src/Exceptions/Configuration/UndefinedDatabaseTypeException.php
new file mode 100644
index 0000000..ada2c85
--- /dev/null
+++ b/src/Exceptions/Configuration/UndefinedDatabaseTypeException.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\Exceptions\Configuration;
+
+use Nest\Database\Exceptions\DatabaseException;
+use Throwable;
+
+/**
+ * Exception thrown when a database type is missing in one of the configurations.
+ */
+class UndefinedDatabaseTypeException extends DatabaseException
+{
+	/**
+	 * @param string $identifier Database identifier with missing type.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $identifier, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/DatabaseException.php b/src/Exceptions/DatabaseException.php
new file mode 100644
index 0000000..9a60cc4
--- /dev/null
+++ b/src/Exceptions/DatabaseException.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace Nest\Database\Exceptions;
+
+use Nest\Exceptions\Exception;
+
+class DatabaseException extends Exception
+{
+}
diff --git a/src/Exceptions/InvalidTransactionStateException.php b/src/Exceptions/InvalidTransactionStateException.php
new file mode 100644
index 0000000..a0b8efb
--- /dev/null
+++ b/src/Exceptions/InvalidTransactionStateException.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Nest\Database\Exceptions;
+
+/**
+ * Exception thrown when the current transaction does not allow to commit or rollback the transaction.
+ */
+class InvalidTransactionStateException extends DatabaseException
+{
+	public function __construct(string $message = "", int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct($message, $code, $previous);
+	}
+}
diff --git a/src/Exceptions/Migrations/CannotRollbackException.php b/src/Exceptions/Migrations/CannotRollbackException.php
new file mode 100644
index 0000000..2d402b6
--- /dev/null
+++ b/src/Exceptions/Migrations/CannotRollbackException.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Database\Exceptions\Migrations;
+
+use Nest\Database\Migrations\Migration;
+use Nest\Database\Exceptions\DatabaseException;
+use Throwable;
+
+/**
+ * Thrown when a migration cannot be rolled back.
+ */
+class CannotRollbackException extends DatabaseException
+{
+	/**
+	 * @param Migration $migration The migration which cannot be rolled back.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public Migration $migration, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Cannot rollback migration {$this->migration->getName()}.", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/Migrations/MigrationNotFoundException.php b/src/Exceptions/Migrations/MigrationNotFoundException.php
new file mode 100644
index 0000000..9e29746
--- /dev/null
+++ b/src/Exceptions/Migrations/MigrationNotFoundException.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\Exceptions\Migrations;
+
+use Nest\Database\Exceptions\DatabaseException;
+use Throwable;
+
+/**
+ * Thrown when a given migration was not found.
+ */
+class MigrationNotFoundException extends DatabaseException
+{
+	/**
+	 * @param string $id Migration ID that wasn't found.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $id, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Migration $this->id not found.", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/Migrations/UndefinedNewColumnTypeException.php b/src/Exceptions/Migrations/UndefinedNewColumnTypeException.php
new file mode 100644
index 0000000..f621035
--- /dev/null
+++ b/src/Exceptions/Migrations/UndefinedNewColumnTypeException.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Database\Exceptions\Migrations;
+
+use Nest\Database\Exceptions\DatabaseException;
+use Throwable;
+
+/**
+ * Exception thrown when a new table column has an undefined type.
+ */
+class UndefinedNewColumnTypeException extends DatabaseException
+{
+	/**
+	 * @param string $tableName Table name.
+	 * @param string $columnName Column name.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $tableName, public string $columnName, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Undefined column type for \"$this->tableName\".\"$this->columnName\".", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/NotCurrentTransactionException.php b/src/Exceptions/NotCurrentTransactionException.php
new file mode 100644
index 0000000..749550c
--- /dev/null
+++ b/src/Exceptions/NotCurrentTransactionException.php
@@ -0,0 +1,26 @@
+<?php
+
+namespace Nest\Database\Exceptions;
+
+use Nest\Database\Transactions\Transaction;
+use Throwable;
+
+/**
+ * Exception thrown when the altered transaction is not the current one.
+ */
+class NotCurrentTransactionException extends DatabaseException
+{
+	/**
+	 * @param Transaction $currentTransaction The current transaction.
+	 * @param Transaction $alteredTransaction The altered transaction.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public Transaction $currentTransaction, public Transaction $alteredTransaction, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct(
+			"Only the current transaction (".$this->currentTransaction->getUuid().") can be altered. Cannot alter ".$this->alteredTransaction->getUuid().".",
+			$code, $previous
+		);
+	}
+}
diff --git a/src/Exceptions/Query/MissingConditionValueException.php b/src/Exceptions/Query/MissingConditionValueException.php
new file mode 100644
index 0000000..42a16e5
--- /dev/null
+++ b/src/Exceptions/Query/MissingConditionValueException.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Nest\Database\Exceptions\Query;
+
+use Throwable;
+
+/**
+ * Exception thrown when no condition value has been given to the condition builder.
+ */
+class MissingConditionValueException extends QueryBuilderException
+{
+	/**
+	 * @param string $incompleteSql Incomplete SQL condition.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $incompleteSql, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Cannot complete SQL condition: $this->incompleteSql", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/Query/NoPrimaryFieldException.php b/src/Exceptions/Query/NoPrimaryFieldException.php
new file mode 100644
index 0000000..e46b3e8
--- /dev/null
+++ b/src/Exceptions/Query/NoPrimaryFieldException.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\Exceptions\Query;
+
+use Nest\Model\Entity;
+use Throwable;
+
+/**
+ * Exception thrown when an entity has no primary fields to use in WHERE clause.
+ */
+class NoPrimaryFieldException extends QueryBuilderException
+{
+	/**
+	 * @param Entity $entity The entity without primary fields.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public Entity $entity, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("No defined primary fields for ".get_class($this->entity).", cannot apply WHERE clause on it.", $code, $previous);
+	}
+}
diff --git a/src/Exceptions/Query/QueryBuilderException.php b/src/Exceptions/Query/QueryBuilderException.php
new file mode 100644
index 0000000..19fedae
--- /dev/null
+++ b/src/Exceptions/Query/QueryBuilderException.php
@@ -0,0 +1,9 @@
+<?php
+
+namespace Nest\Database\Exceptions\Query;
+
+use Nest\Database\Exceptions\DatabaseException;
+
+class QueryBuilderException extends DatabaseException
+{
+}
diff --git a/src/Exceptions/UnknownDatabaseException.php b/src/Exceptions/UnknownDatabaseException.php
new file mode 100644
index 0000000..1b34e43
--- /dev/null
+++ b/src/Exceptions/UnknownDatabaseException.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Nest\Database\Exceptions;
+
+use Throwable;
+
+/**
+ * Exception thrown when a requested database is unknown.
+ */
+class UnknownDatabaseException extends DatabaseException
+{
+	/**
+	 * @param string $identifier Database identifier.
+	 * @param int $code [optional] The Exception code.
+	 * @param null|Throwable $previous [optional] The previous throwable used for the exception chaining.
+	 */
+	public function __construct(public string $identifier, int $code = 0, ?Throwable $previous = null)
+	{
+		parent::__construct("Unknown database $this->identifier.", $code, $previous);
+	}
+}
diff --git a/src/Migrations/Configuration/MigrationsConfiguration.php b/src/Migrations/Configuration/MigrationsConfiguration.php
new file mode 100644
index 0000000..49261a9
--- /dev/null
+++ b/src/Migrations/Configuration/MigrationsConfiguration.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Nest\Database\Migrations\Configuration;
+
+use Nest\Services\ServiceConfiguration;
+use function Nest\Utils\path_join;
+
+/**
+ * Migrations configuration class.
+ */
+abstract class MigrationsConfiguration extends ServiceConfiguration
+{
+	/**
+	 * @return string Database migrations PHP namespace.
+	 */
+	public abstract function getMigrationsNamespace(): string;
+
+	/**
+	 * @return string Database migrations path.
+	 */
+	public abstract function getMigrationsPath(): string;
+
+	/**
+	 * @return string Database preparations path.
+	 */
+	public function getPreparationsPath(): string
+	{
+		return path_join($this->getMigrationsPath(), "Prepare");
+	}
+
+	/**
+	 * Get database to use for migrations table.
+	 * @return string Database identifier.
+	 */
+	public function getMigrationsDatabase(): string
+	{
+		return "default";
+	}
+
+	/**
+	 * @return string Done migrations table name.
+	 */
+	public function getMigrationsTable(): string
+	{
+		return "_migrations";
+	}
+}
diff --git a/src/Migrations/Configuration/MigrationsConfigurator.php b/src/Migrations/Configuration/MigrationsConfigurator.php
new file mode 100644
index 0000000..06313d0
--- /dev/null
+++ b/src/Migrations/Configuration/MigrationsConfigurator.php
@@ -0,0 +1,106 @@
+<?php
+
+namespace Nest\Database\Migrations\Configuration;
+
+/**
+ * Migrations configurator.
+ */
+class MigrationsConfigurator extends MigrationsConfiguration
+{
+	private string $migrationsNamespace;
+	private string $migrationsPath;
+	private string $preparationsPath;
+	private string $migrationsDatabase;
+	private string $migrationsTable;
+
+	/**
+	 * @param string $migrationsNamespace Database migrations PHP namespace.
+	 * @return $this
+	 */
+	public function setMigrationsNamespace(string $migrationsNamespace): static
+	{
+		$this->migrationsNamespace = $migrationsNamespace;
+		return $this;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function getMigrationsNamespace(): string
+	{
+		return $this->migrationsNamespace;
+	}
+
+	/**
+	 * @param string $migrationsPath Database migrations path.
+	 * @return $this
+	 */
+	public function setMigrationsPath(string $migrationsPath): static
+	{
+		$this->migrationsPath = $migrationsPath;
+		return $this;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function getMigrationsPath(): string
+	{
+		return $this->migrationsPath;
+	}
+
+	/**
+	 * @param string $preparationsPath Database preparations path.
+	 * @return $this
+	 */
+	public function setPreparationsPath(string $preparationsPath): static
+	{
+		$this->preparationsPath = $preparationsPath;
+		return $this;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function getPreparationsPath(): string
+	{
+		return $this->preparationsPath ?? parent::getPreparationsPath();
+	}
+
+	/**
+	 * Set database to use for migrations table.
+	 * @param string $databaseIdentifier Database identifier.
+	 * @return $this
+	 */
+	public function setMigrationsDatabase(string $databaseIdentifier): static
+	{
+		$this->migrationsDatabase = $databaseIdentifier;
+		return $this;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	public function getMigrationsDatabase(): string
+	{
+		return $this->migrationsDatabase ?? parent::getMigrationsDatabase();
+	}
+
+	/**
+	 * @param string $migrationsTable Done migrations table name.
+	 * @return $this
+	 */
+	public function setMigrationsTable(string $migrationsTable): static
+	{
+		$this->migrationsTable = $migrationsTable;
+		return $this;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function getMigrationsTable(): string
+	{
+		return $this->migrationsTable ?? parent::getMigrationsTable();
+	}
+}
diff --git a/src/Migrations/Diff/Table.php b/src/Migrations/Diff/Table.php
new file mode 100644
index 0000000..893d295
--- /dev/null
+++ b/src/Migrations/Diff/Table.php
@@ -0,0 +1,137 @@
+<?php
+
+namespace Nest\Database\Migrations\Diff;
+
+use Nest\Database\Database;
+
+/**
+ * Table modifications manager.
+ */
+class Table
+{
+	/**
+	 * @param Database $database The database on which to perform operations on the given table.
+	 * @param string $tableName Name of the table to modify.
+	 */
+	public function __construct(protected Database $database, protected string $tableName)
+	{}
+
+	/**
+	 * The database on which to perform operations on the table.
+	 * @return Database
+	 */
+	public function getDatabase(): Database
+	{
+		return $this->database;
+	}
+
+	/**
+	 * Get table name.
+	 * @return string
+	 */
+	public function getTableName(): string
+	{
+		return $this->tableName;
+	}
+
+	/**
+	 * Create the table.
+	 * @param bool $ifNotExists True to try to add if table does not exist, will just pass if it exists.
+	 * @return $this
+	 */
+	public function create(bool $ifNotExists = false): static
+	{
+		$this->getDatabase()->getQueriesAdapter()->createTable($this->getTableName(), $ifNotExists);
+		return $this;
+	}
+
+	/**
+	 * Create the table, if it does not exists.
+	 * @return $this
+	 */
+	public function createIfNotExists(): static
+	{
+		return $this->create(true);
+	}
+
+	/**
+	 * Drop the table.
+	 * @param bool $ifExists True to try to drop if table exists, will just pass if it does not exist.
+	 * @return $this
+	 */
+	public function drop(bool $ifExists = false): static
+	{
+		$this->getDatabase()->getQueriesAdapter()->dropTable($this->getTableName(), $ifExists);
+		return $this;
+	}
+
+	/**
+	 * Drop the table, if it exists.
+	 * @return $this
+	 */
+	public function dropIfExists(): static
+	{
+		return $this->drop(true);
+	}
+
+	/**
+	 * Rename the table.
+	 * @param string $newName New name of the table.
+	 * @return void
+	 */
+	public function rename(string $newName): void
+	{
+		$this->getDatabase()->getQueriesAdapter()->renameTable($this->getTableName(), $newName);
+	}
+
+
+	/**
+	 * Get or create a column for the current table.
+	 * @param string $columnName Column name.
+	 * @return TableColumn The table column.
+	 */
+	public function column(string $columnName): TableColumn
+	{
+		return new TableColumn($this, $columnName);
+	}
+
+	/**
+	 * Make a foreign key creator for the current table.
+	 * @return TableForeignKey The table foreign key creator.
+	 */
+	public function foreignKey(): TableForeignKey
+	{
+		return new TableForeignKey($this);
+	}
+
+	/**
+	 * Get or create an index for the current table.
+	 * @param string $indexName Index name.
+	 * @return TableIndex The table index.
+	 */
+	public function index(string $indexName): TableIndex
+	{
+		return new TableIndex($this, $indexName);
+	}
+
+	/**
+	 * Drop a constraint with the given name.
+	 * @param string $constraintName The constraint to drop.
+	 * @param bool $ifExists True to try to drop if constraint exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public function dropConstraint(string $constraintName, bool $ifExists = false): void
+	{
+		$this->getDatabase()->getQueriesAdapter()->dropConstraint($this->getTableName(), $constraintName, $ifExists);
+	}
+
+	/**
+	 * Drop a constraint with the given name if it exists.
+	 * @param string $constraintName The constraint to drop.
+	 * @return void
+	 */
+	public function dropConstraintIfExists(string $constraintName): void
+	{
+		$this->dropConstraint($constraintName, true);
+	}
+}
diff --git a/src/Migrations/Diff/TableColumn.php b/src/Migrations/Diff/TableColumn.php
new file mode 100644
index 0000000..1893a01
--- /dev/null
+++ b/src/Migrations/Diff/TableColumn.php
@@ -0,0 +1,188 @@
+<?php
+
+namespace Nest\Database\Migrations\Diff;
+
+use BackedEnum;
+use Nest\Database\Query\Raw;
+use Nest\Database\Exceptions\Migrations\UndefinedNewColumnTypeException;
+use Stringable;
+
+/**
+ * Table column class.
+ */
+class TableColumn
+{
+	/**
+	 * SQL type of the column.
+	 * @var string
+	 */
+	public string $type;
+
+	/**
+	 * Column index definition.
+	 * @var TableColumnIndex
+	 */
+	public TableColumnIndex $index;
+
+	/**
+	 * Column is a primary key.
+	 * @var bool
+	 */
+	public bool $primary;
+
+	/**
+	 * Default column value.
+	 * @var Raw|string|int|float|null
+	 */
+	public Raw|string|int|float|null $default;
+
+	/**
+	 * Is column nullable or not.
+	 * @var bool
+	 */
+	public bool $nullable;
+
+	/**
+	 * Create a new table column.
+	 * @param Table $table Table of the column.
+	 * @param string $name Column name.
+	 */
+	public function __construct(public readonly Table $table, public readonly string $name)
+	{
+	}
+
+	/**
+	 * Set the SQL type of the column.
+	 * @param string|Stringable|BackedEnum $type SQL type of the column.
+	 * @return $this
+	 */
+	public function type(string|Stringable|BackedEnum $type): static
+	{
+		$this->type = (string) ($type instanceof BackedEnum ? $type->value : $type);
+		return $this;
+	}
+
+	/**
+	 * Set default column value.
+	 * @param Raw|string|int|float|null $value Default column value.
+	 * @return $this
+	 */
+	public function default(Raw|string|int|float|null $value): static
+	{
+		$this->default = $value;
+		return $this;
+	}
+
+	/**
+	 * Set default column value to NOW.
+	 * @return $this
+	 */
+	public function defaultNow(): static
+	{
+		return $this->default(new Raw("NOW()"));
+	}
+
+	/**
+	 * Set nullable for the current column.
+	 * @param bool $nullable True if the column is nullable, false otherwise.
+	 * @return $this
+	 */
+	public function nullable(bool $nullable = true): static
+	{
+		$this->nullable = $nullable;
+		return $this;
+	}
+
+	/**
+	 * Current column is a primary key.
+	 * @return $this
+	 */
+	public function primary(): static
+	{
+		// Set the current column as a primary key.
+		$this->primary = true;
+		return $this;
+	}
+
+	/**
+	 * Index the current column.
+	 * @param bool $unique True to ensure a unique value for each row, false otherwise.
+	 * @param string|null $method Custom index method (raw SQL!).
+	 * @return $this
+	 */
+	public function index(bool $unique = false, ?string $method = null): static
+	{
+		// Initialize the column index.
+		$this->index = new TableColumnIndex();
+		$this->index->unique = $unique;
+		if (!empty($method)) $this->index->method = $method;
+		return $this;
+	}
+
+	/**
+	 * Unique index the current column.
+	 * @param string|null $method Custom index method (raw SQL!).
+	 * @return $this
+	 */
+	public function unique(?string $method = null): static
+	{
+		// Initialize the column index.
+		return $this->index(true, $method);
+	}
+
+	/**
+	 * Add the current column to the table.
+	 * @param bool $ifNotExists True to try to add if column does not exist, will just pass if it exists.
+	 * @return void
+	 * @throws UndefinedNewColumnTypeException
+	 */
+	public function add(bool $ifNotExists = false): void
+	{
+		if (empty($this->type))
+			// Throw an exception if no type is provided.
+			throw new UndefinedNewColumnTypeException($this->table->getTableName(), $this->name);
+
+		// Add table column.
+		$this->table->getDatabase()->getQueriesAdapter()->addTableColumn($this, $ifNotExists);
+
+		// Set column index, if it's defined.
+		if (!empty($this->index))
+			$this->table->getDatabase()->getQueriesAdapter()->setTableColumnIndex($this);
+	}
+
+	/**
+	 * Rename the column.
+	 * @param string $newName New name of the column.
+	 * @return void
+	 */
+	public function rename(string $newName): void
+	{
+		// Rename table column.
+		$this->table->getDatabase()->getQueriesAdapter()->renameTableColumn($this, $newName);
+	}
+
+	/**
+	 * Alter the current table column.
+	 * @return void
+	 */
+	public function alter(): void
+	{
+		// Alter table column.
+		$this->table->getDatabase()->getQueriesAdapter()->alterTableColumn($this);
+
+		// Set column index, if it's defined.
+		if (!empty($this->index))
+			$this->table->getDatabase()->getQueriesAdapter()->setTableColumnIndex($this);
+	}
+
+	/**
+	 * Drop the current column from the table.
+	 * @param bool $ifExists True to try to drop if column exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public function drop(bool $ifExists = false): void
+	{
+		// Drop table column.
+		$this->table->getDatabase()->getQueriesAdapter()->dropTableColumn($this->table->getTableName(), $this->name, $ifExists);
+	}
+}
diff --git a/src/Migrations/Diff/TableColumnIndex.php b/src/Migrations/Diff/TableColumnIndex.php
new file mode 100644
index 0000000..7b00b35
--- /dev/null
+++ b/src/Migrations/Diff/TableColumnIndex.php
@@ -0,0 +1,21 @@
+<?php
+
+namespace Nest\Database\Migrations\Diff;
+
+/**
+ * Table column index definition.
+ */
+class TableColumnIndex
+{
+	/**
+	 * Unique key index.
+	 * @var bool
+	 */
+	public bool $unique = false;
+
+	/**
+	 * Custom index method (raw SQL!).
+	 * @var string
+	 */
+	public string $method;
+}
diff --git a/src/Migrations/Diff/TableForeignKey.php b/src/Migrations/Diff/TableForeignKey.php
new file mode 100644
index 0000000..3c3d023
--- /dev/null
+++ b/src/Migrations/Diff/TableForeignKey.php
@@ -0,0 +1,102 @@
+<?php
+
+namespace Nest\Database\Migrations\Diff;
+
+/**
+ * Table foreign key configurator.
+ */
+class TableForeignKey
+{
+	/**
+	 * Foreign key columns.
+	 * @var string[]
+	 */
+	public array $columns = [];
+
+	/**
+	 * Referenced table.
+	 * @var string
+	 */
+	public string $referencedTable;
+
+	/**
+	 * Referenced columns.
+	 * @var string[]
+	 */
+	public array $referencedColumns;
+
+	/**
+	 * Action on delete.
+	 * @var string
+	 */
+	public string $onDelete;
+	/**
+	 * Action on update.
+	 * @var string
+	 */
+	public string $onUpdate;
+
+	/**
+	 * Create a new table foreign key.
+	 * @param Table $table Table of the foreign key.
+	 */
+	public function __construct(public readonly Table $table)
+	{
+	}
+
+	/**
+	 * Add foreign key columns.
+	 * @param string ...$columns Foreign key columns.
+	 * @return $this
+	 */
+	public function columns(string ...$columns): static
+	{
+		array_push($this->columns, ...$columns);
+		return $this;
+	}
+
+	/**
+	 * Set referenced table and columns..
+	 * @param string $referencedTable Referenced table name.
+	 * @param string[] $referencedColumns Referenced columns in table.
+	 * @return $this
+	 */
+	public function references(string $referencedTable, string ...$referencedColumns): static
+	{
+		$this->referencedTable = $referencedTable;
+		$this->referencedColumns = $referencedColumns;
+
+		return $this;
+	}
+
+	/**
+	 * Set action on delete.
+	 * @param string $referentialAction Raw action.
+	 * @return $this
+	 */
+	public function onDelete(string $referentialAction): static
+	{
+		$this->onDelete = $referentialAction;
+		return $this;
+	}
+
+	/**
+	 * Set action on update.
+	 * @param string $referentialAction Raw action.
+	 * @return $this
+	 */
+	public function onUpdate(string $referentialAction): static
+	{
+		$this->onUpdate = $referentialAction;
+		return $this;
+	}
+
+	/**
+	 * Create the defined foreign key.
+	 * @return void
+	 */
+	public function create(): void
+	{
+		$this->table->getDatabase()->getQueriesAdapter()->createForeignKey($this);
+	}
+}
diff --git a/src/Migrations/Diff/TableIndex.php b/src/Migrations/Diff/TableIndex.php
new file mode 100644
index 0000000..162d3e8
--- /dev/null
+++ b/src/Migrations/Diff/TableIndex.php
@@ -0,0 +1,167 @@
+<?php
+
+namespace Nest\Database\Migrations\Diff;
+
+/**
+ * Table index class.
+ */
+class TableIndex
+{
+	/**
+	 * Index columns.
+	 * @var string[]
+	 */
+	public array $columns;
+
+	/**
+	 * Raw expression to index.
+	 * @var string|null
+	 */
+	public ?string $rawExpression = null;
+
+	/**
+	 * Whether indexed values must be uniques or not.
+	 * @var bool
+	 */
+	public bool $unique = false;
+
+	/**
+	 * Index method to use.
+	 * @var string|null
+	 */
+	public ?string $method = null;
+
+	/**
+	 * ASC or DESC.
+	 * @var string|null
+	 */
+	public ?string $order = null;
+
+	/**
+	 * NULLS FIRST or NULLS LAST.
+	 * @var string|null
+	 */
+	public ?string $nulls = null;
+
+	/**
+	 * Create a new table index.
+	 * @param Table $table Table of the index.
+	 * @param string $name Index name.
+	 */
+	public function __construct(public readonly Table $table, public readonly string $name)
+	{
+	}
+
+	/**
+	 * Add columns in the index.
+	 * @param string ...$columns Columns to add in the index.
+	 * @return $this
+	 */
+	public function columns(string ...$columns): static
+	{
+		array_push($this->columns, ...$columns);
+		return $this;
+	}
+
+	/**
+	 * Set a raw expression to index.
+	 * @param string $rawExpression Raw expression to index.
+	 * @return $this
+	 */
+	public function expression(string $rawExpression): static
+	{
+		$this->rawExpression = $rawExpression;
+		return $this;
+	}
+
+	/**
+	 * Set that indexed values must be uniques.
+	 * @param bool $unique True to set unique, false to set non-unique.
+	 * @return $this
+	 */
+	public function unique(bool $unique = true): static
+	{
+		$this->unique = $unique;
+		return $this;
+	}
+
+	/**
+	 * Set the method to used to index.
+	 * @param string|null $method Index method to use.
+	 * @return $this
+	 */
+	public function using(?string $method): static
+	{
+		$this->method = $method;
+		return $this;
+	}
+
+	/**
+	 * Ascending sort order.
+	 * @return $this
+	 */
+	public function asc(): static
+	{
+		$this->order = "ASC";
+		return $this;
+	}
+	/**
+	 * Descending sort order.
+	 * @return $this
+	 */
+	public function desc(): static
+	{
+		$this->order = "DESC";
+		return $this;
+	}
+
+	/**
+	 * Nulls sort before non-nulls.
+	 * @return $this
+	 */
+	public function nullsFirst(): static
+	{
+		$this->nulls = "NULLS FIRST";
+		return $this;
+	}
+	/**
+	 * Nulls sort after non-nulls.
+	 * @return $this
+	 */
+	public function nullsLast(): static
+	{
+		$this->nulls = "NULLS LAST";
+		return $this;
+	}
+
+	/**
+	 * Create index.
+	 * @param bool $ifNotExists True to try to add if index does not exist, will just pass if it exists.
+	 * @return void
+	 */
+	public function create(bool $ifNotExists = false): void
+	{
+		$this->table->getDatabase()->getQueriesAdapter()->createIndex($this, $ifNotExists);
+	}
+
+	/**
+	 * Rename index.
+	 * @param string $newName The new name of the index.
+	 * @param bool $ifExists True to try to rename if index exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public function renameTo(string $newName, bool $ifExists = false): void
+	{
+		$this->table->getDatabase()->getQueriesAdapter()->renameIndex($this->name, $newName, $ifExists);
+	}
+
+	/**
+	 * Drop index.
+	 * @param bool $ifExists True to try to drop if index exists, will just pass if it does not exist.
+	 * @return void
+	 */
+	public function drop(bool $ifExists = false): void
+	{
+		$this->table->getDatabase()->getQueriesAdapter()->dropIndex($this, $ifExists);
+	}
+}
diff --git a/src/Migrations/Migration.php b/src/Migrations/Migration.php
new file mode 100644
index 0000000..d7ed328
--- /dev/null
+++ b/src/Migrations/Migration.php
@@ -0,0 +1,67 @@
+<?php
+
+namespace Nest\Database\Migrations;
+
+use Nest\Database\Database;
+use Nest\Database\Migrations\Diff\Table;
+
+/**
+ * A database migration.
+ */
+abstract class Migration
+{
+
+	/**
+	 * Construct a new database migration.
+	 * @param Database $database The database of the migration.
+	 * @param string $version Version identifier.
+	 * @param string $name Database migration name.
+	 */
+	public function __construct(protected readonly Database $database, private readonly string $version, private readonly string $name)
+	{
+	}
+
+	/**
+	 * @return string The version identifier.
+	 */
+	public function getVersion(): string
+	{
+		return $this->version;
+	}
+	/**
+	 * @return string The database migration name.
+	 */
+	public function getName(): string
+	{
+		return $this->name;
+	}
+
+	/**
+	 * Describes operations of the current database migration.
+	 * @return string Description of database migration.
+	 */
+	public abstract function getDescription(): string;
+
+	/**
+	 * Do the migration.
+	 * @return void
+	 */
+	public abstract function up(): void;
+
+	/**
+	 * Undo the migration.
+	 * @return void
+	 */
+	public abstract function down(): void;
+
+
+	/**
+	 * Create a new table diff manager.
+	 * @param string $tableName Table name to alter.
+	 * @return Table Table diff manager.
+	 */
+	protected function table(string $tableName): Table
+	{
+		return new Table($this->database, $tableName);
+	}
+}
diff --git a/src/Migrations/Migrations.php b/src/Migrations/Migrations.php
new file mode 100644
index 0000000..a2a2d9a
--- /dev/null
+++ b/src/Migrations/Migrations.php
@@ -0,0 +1,572 @@
+<?php
+
+namespace Nest\Database\Migrations;
+
+use Nest\Application;
+use Nest\Database\Database;
+use Nest\Database\Migrations\Configuration\MigrationsConfiguration;
+use DateTime;
+use Nest\Database\Migrations\Diff\Table;
+use Nest\Database\PostgreSql\Columns\Timestamp;
+use Nest\Database\PostgreSql\Columns\Type;
+use Nest\Database\Exceptions\Migrations\MigrationNotFoundException;
+use Nest\Database\Exceptions\Migrations\UndefinedNewColumnTypeException;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+use Nest\Database\Exceptions\UnknownDatabaseException;
+use Nest\Exceptions\InvalidTypeException;
+use Nest\Model\Exceptions\MissingRequiredFieldException;
+use Nest\Model\Exceptions\UndefinedRelationException;
+use Nest\Model\Exceptions\UnhandledPropertyTypeException;
+use Nest\Types\Exceptions\IncompatibleTypeException;
+use Nest\Model\EntityBlueprint;
+use Throwable;
+use function Nest\Utils\path_join;
+
+class Migrations
+{
+	/**
+	 * The database on which to execute the migrations.
+	 * @var Database
+	 */
+	protected Database $database;
+
+	/**
+	 * The migrations array.
+	 * Indexed by their version identifier.
+	 * @var array<string, array>
+	 */
+	private array $migrations = [];
+
+	/**
+	 * The preparations scripts array.
+	 * @var string[]
+	 */
+	private array $preparations = [];
+
+	/**
+	 * Migration start event.
+	 * @var callable(Migration): void|null
+	 */
+	public $onMigrationStart = null;
+
+	/**
+	 * Migration end event.
+	 * @var callable(Migration): void|null
+	 */
+	public $onMigrationEnd = null;
+
+	/**
+	 * Rollback start event.
+	 * @var callable(Migration): void|null
+	 */
+	public $onRollbackStart = null;
+
+	/**
+	 * Rollback end event.
+	 * @var callable(Migration): void|null
+	 */
+	public $onRollbackEnd = null;
+
+	/**
+	 * @param Application $application The application.
+	 * @param MigrationsConfiguration $configuration The migrations configuration.
+	 */
+	public function __construct(protected Application $application, protected MigrationsConfiguration $configuration)
+	{
+	}
+
+	/**
+	 * Initial load of the migrations system.
+	 * @return $this
+	 * @throws IncompatibleTypeException
+	 * @throws MissingConditionValueException
+	 * @throws UnknownDatabaseException
+	 * @throws UndefinedNewColumnTypeException
+	 */
+	public function load(): static
+	{
+		// Get migrations database.
+		$this->database = $this->application->databases()->db($this->configuration->getMigrationsDatabase());
+
+		// Initial load of database migrations and preparations.
+		$this->prepareMigrationsTable();
+		$this->loadMigrations();
+		$this->loadPreparations();
+
+		return $this;
+	}
+
+	/**
+	 * Try to register a new migration file.
+	 * @param string $migrationFile The migration file name.
+	 * @param string $subdirectory Subdirectory where the migration file has been found.
+	 * @return void
+	 */
+	protected function registerMigration(string $migrationFile, string $subdirectory): void
+	{
+		if (preg_match("/^V([0-9]+)_([^.]+)\\.php$/", $migrationFile, $matches))
+		{ // The filename matches migration name format.
+			$version = $matches[1];
+			$name = $matches[2];
+
+			$this->migrations[$version] = [
+				"version" => $version,
+				"name" => $name,
+				"migrated" => false, // Already run migrations are found by using findMigrated after migration registration.
+				"entity" => null, // Migration entity in database, when it's migrated.
+				"package" => $subdirectory,
+			];
+		}
+	}
+
+	/**
+	 * Recursively load migrations in the given path with subdirectory.
+	 * @param string $migrationsPath The path where to find migrations.
+	 * @param string $subdirectory The subdirectory / subpackage of registered migration files.
+	 * @return void
+	 */
+	private function _loadMigrations(string $migrationsPath, string $subdirectory = ""): void
+	{
+		// Get the list of files in the migrations directory.
+		$migrationFiles = scandir($migrationsPath);
+
+		foreach ($migrationFiles as $migrationFile)
+		{ // Try to register each migration file.
+			$migrationFileFullPath = path_join($migrationsPath, $migrationFile);
+			if (is_dir($migrationFileFullPath) && $migrationFile != "." && $migrationFile != "..")
+			{ // If it is a directory, we try to read it recursively.
+				$this->_loadMigrations($migrationFileFullPath, !empty($subdirectory) ? path_join($subdirectory, $migrationFile) : $migrationFile);
+			}
+			else
+			{ // It is a file, we try to register it as a migration file.
+				$this->registerMigration($migrationFile, $subdirectory);
+			}
+		}
+	}
+
+	/**
+	 * Load all existing migrations.
+	 * @return void
+	 * @throws IncompatibleTypeException
+	 * @throws MissingConditionValueException
+	 */
+	protected function loadMigrations(): void
+	{
+		// Reset migrations list.
+		$this->migrations = [];
+
+		// Load migrations in the configured migrations path.
+		$this->_loadMigrations($this->configuration->getMigrationsPath());
+
+		// Sort migrations by lexicographic order of version identifiers.
+		ksort($this->migrations);
+
+		// Find done migrations.
+		$this->findMigrated();
+	}
+
+	/**
+	 * Load all preparations scripts.
+	 * @return void
+	 */
+	protected function loadPreparations(): void
+	{
+		// Reset preparations scripts list.
+		$this->preparations = [];
+
+		if (file_exists($this->configuration->getPreparationsPath()))
+		{ // If there is a preparation folder.
+
+			// Get all preparations scripts files.
+			$this->preparations = scandir($this->configuration->getPreparationsPath());
+
+			// Filter non-SQL files.
+			$this->preparations = array_filter($this->preparations, fn ($preparationScript) => (
+				// Only keep files ending with ".sql".
+				is_file($preparationScript) && str_ends_with($preparationScript, ".sql")
+			));
+
+			// Sort in lexicographic order.
+			sort($this->preparations);
+		}
+	}
+
+	/**
+	 * Prepare migrations table: create it if it doesn't exists.
+	 * @return void
+	 * @throws UndefinedNewColumnTypeException
+	 */
+	protected function prepareMigrationsTable(): void
+	{
+		$table = new Table($this->database, $this->configuration->getMigrationsTable());
+		$table->createIfNotExists();
+		$table->column("id")->type(Type::Varchar)->primary()->add(true);
+		$table->column("name")->type(Type::Varchar)->index()->add(true);
+		$table->column("created_at")->type(new Timestamp(true))->defaultNow()->add(true);
+	}
+
+	/**
+	 * Get a migration model for the current migrations.
+	 * @return \Nest\Database\Migrations\Model\Migration
+	 */
+	protected function getMigrationModel(): \Nest\Database\Migrations\Model\Migration
+	{
+		// Create an anonymous class for the current migrations.
+		$migrationModel = new class extends \Nest\Database\Migrations\Model\Migration
+		{
+			/**
+			 * Migrations table name.
+			 * @var string
+			 */
+			public static string $migrationsTableName;
+
+			/**
+			 * @inheritDoc
+			 */
+			public function definition(EntityBlueprint $blueprint): EntityBlueprint
+			{
+				if (!empty(static::$migrationsTableName))
+					// Set migrations table name.
+					$blueprint->setTable(static::$migrationsTableName);
+
+				return parent::definition($blueprint);
+			}
+		};
+
+		// Set migrations table name.
+		// $migrationModel cannot be used as is: the table name has been defined after the first definition.
+		$migrationModel::$migrationsTableName = $this->configuration->getMigrationsTable();
+
+		return $migrationModel->new(); // Return migrations model base instance.
+	}
+
+	/**
+	 * Find done migrations.
+	 * @return void
+	 * @throws IncompatibleTypeException
+	 * @throws MissingConditionValueException
+	 * @throws UnknownDatabaseException
+	 * @throws InvalidTypeException
+	 * @throws UndefinedRelationException
+	 * @throws UnhandledPropertyTypeException
+	 */
+	protected function findMigrated(): void
+	{
+		/**
+		 * Get migrated migrations.
+		 * @var \Nest\Database\Migrations\Model\Migration[] $migrations
+		 */
+		$migrations = $this->getMigrationModel()->query()->get();
+
+		foreach ($migrations as $migration)
+		{ // Set each migration as migrated.
+			$this->migrations[$migration->id]["migrated"] = true;
+			$this->migrations[$migration->id]["entity"] = $migration;
+		}
+	}
+
+	/**
+	 * Mark the given migration as migrated.
+	 * @param string $migrationId The migration version identifier.
+	 * @return void
+	 * @throws IncompatibleTypeException
+	 * @throws MissingConditionValueException
+	 * @throws UnknownDatabaseException
+	 * @throws MissingRequiredFieldException
+	 */
+	public function markMigrated(string $migrationId): void
+	{
+		// Mark migration as migrated.
+		$this->migrations[$migrationId]["migrated"] = true;
+
+		// Create a migration and save it as migrated.
+		$this->migrations[$migrationId]["entity"] = $this->getMigrationModel()->new();
+		$this->migrations[$migrationId]["entity"]->id = $migrationId;
+		$this->migrations[$migrationId]["entity"]->name = $this->migrations[$migrationId]["name"];
+		$this->migrations[$migrationId]["entity"]->save();
+	}
+	/**
+	 * Mark the given migration as NOT migrated.
+	 * @param string $migrationId The migration version identifier.
+	 * @return void
+	 */
+	public function markNotMigrated(string $migrationId): void
+	{
+		$this->migrations[$migrationId]["entity"]->delete();
+		$this->migrations[$migrationId]["migrated"] = false;
+	}
+
+	/**
+	 * Get a new version for a new database migration.
+	 * @return string The version of a new migration.
+	 */
+	protected function getNewVersion(): string
+	{
+		// Generate a new version from current date and time.
+		return (new DateTime())->format("YmdHis");
+	}
+
+	/**
+	 * Generate a new migration with the given name.
+	 * @param string $migrationName The migration name.
+	 * @return void
+	 */
+	public function newMigration(string $migrationName): void
+	{
+		// Database migration filename.
+		$filename = path_join($this->configuration->getMigrationsPath(), "V".($version = $this->getNewVersion()))."_{$migrationName}.php";
+		// Generate new migration content.
+		file_put_contents($filename, <<<EOD
+<?php
+
+declare(strict_types=1);
+
+namespace {$this->configuration->getMigrationsNamespace()};
+
+use Nest\Database\Migrations\Migration;
+
+final class V{$version}_{$migrationName} extends Migration
+{
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function getDescription(): string
+	{ return ""; }
+	
+	/**
+	 * @inheritDoc
+	 */
+	public function up(): void
+	{}
+	
+	/**
+	 * @inheritDoc
+	 */
+	public function down(): void
+	{
+		throw new \Nest\Database\Exceptions\Migrations\CannotRollbackException(\$this);
+	}
+}
+EOD
+);
+	}
+
+	/**
+	 * Get migrations versions list.
+	 * @return string[]
+	 */
+	public function getMigrations(): array
+	{
+		return array_keys($this->migrations);
+	}
+
+	/**
+	 * Construct a new migration instance from its version identifier.
+	 * @param array $migrationData Migration data associative array.
+	 * @return Migration The migration instance.
+	 */
+	protected function newMigrationInstance(array $migrationData): Migration
+	{
+		// Get migration full class name.
+		$fullClassName = "\\".$this->configuration->getMigrationsNamespace()
+			// Add subpackage if there is one.
+			.(!empty($migrationData["package"]) ? "\\".$migrationData["package"] : "")
+			// Add migration class name.
+			."\\V{$migrationData["version"]}_{$migrationData["name"]}";
+
+		// Instantiate migration.
+		return new $fullClassName($this->database, $migrationData["version"], $migrationData["name"]);
+	}
+
+	/**
+	 * Execute a migration.
+	 * @param string $migrationId The migration version identifier.
+	 * @return Migration The executed migration instance.
+	 * @throws IncompatibleTypeException
+	 * @throws MigrationNotFoundException
+	 * @throws MissingConditionValueException
+	 * @throws MissingRequiredFieldException
+	 * @throws UnknownDatabaseException
+	 * @throws Throwable
+	 */
+	public function migrateOne(string $migrationId): Migration
+	{
+		if (empty($this->migrations[$migrationId]))
+			// Migration not found.
+			throw new MigrationNotFoundException($migrationId);
+
+		// Migrate in a transaction.
+		return $this->database->transaction(function () use ($migrationId) {
+			// Get the migration instance.
+			$migration = $this->newMigrationInstance($this->migrations[$migrationId]);
+
+			if (!empty($this->onMigrationStart))
+				// Fire migration start event, if it is defined.
+				($this->onMigrationStart)($migration);
+
+			// Execute migration.
+			$migration->up();
+
+			// Mark the migration as migrated.
+			$this->markMigrated($migrationId);
+
+			if (!empty($this->onMigrationEnd))
+				// Fire migration end event, if it is defined.
+				($this->onMigrationEnd)($migration);
+
+			// Return executed migration.
+			return $migration;
+		});
+	}
+
+	/**
+	 * Execute all unapplied migrations.
+	 * @return Migration[] The applied migrations list.
+	 * @throws IncompatibleTypeException
+	 * @throws MigrationNotFoundException
+	 * @throws MissingConditionValueException
+	 * @throws MissingRequiredFieldException
+	 * @throws UnknownDatabaseException
+	 * @throws Throwable
+	 */
+	public function migrate(): array
+	{
+		// Migrate in a transaction.
+		return $this->database->transaction(function () {
+			// Initialize the executed migrations.
+			$migrated = [];
+
+			// Clear preparations before executing migrations.
+			$this->clearPreparations();
+
+			foreach ($this->migrations as $version => $migration)
+			{ // For each migration, if it is not executed, we execute it.
+				if (!$migration["migrated"])
+				{ // If the migration isn't done, execute it.
+					$migrated[$version] = $this->migrateOne($version);
+				}
+			}
+
+			// Do database preparations after migrations.
+			$this->prepare();
+
+			return $migrated; // Return executed migrations list.
+		});
+	}
+
+	/**
+	 * Rollback a migration.
+	 * @param string $migrationId The migration version identifier.
+	 * @return Migration The rolled back migration.
+	 * @throws MigrationNotFoundException
+	 * @throws Throwable
+	 */
+	public function rollbackOne(string $migrationId): Migration
+	{
+		if (empty($this->migrations[$migrationId]))
+			// Migration not found.
+			throw new MigrationNotFoundException($migrationId);
+
+		// Rollback in a transaction.
+		return $this->database->transaction(function () use ($migrationId) {
+			// Clear preparations before rolling back.
+			$this->clearPreparations();
+
+			// Get the migration instance.
+			$migration = $this->newMigrationInstance($this->migrations[$migrationId]);
+
+			if (!empty($this->onRollbackStart))
+				// Fire rollback start event, if it is defined.
+				($this->onRollbackStart)($migration);
+
+			// Rollback migration.
+			$migration->down();
+
+			// Mark the migration as not migrated.
+			$this->markNotMigrated($migrationId);
+
+			// Do database preparations after rollback.
+			$this->prepare();
+
+			if (!empty($this->onRollbackEnd))
+				// Fire rollback start event, if it is defined.
+				($this->onRollbackEnd)($migration);
+
+			return $migration; // Return rolled back migration.
+		});
+	}
+
+	/**
+	 * Rollback the latest migrated migration
+	 * @return Migration|null The rolled back migration, if there is one.
+	 * @throws MigrationNotFoundException
+	 * @throws Throwable
+	 */
+	public function rollbackLatest(): ?Migration
+	{
+		// Get latest migration ID.
+		$latestMigration = null;
+		foreach (array_reverse($this->migrations, true) as $migrationId => $migration)
+		{ // Exploring migrations in reverse order (the most recent first).
+			if ($migration["migrated"])
+			{ // The first migrated migration is taken as the latest one.
+				$latestMigration = $migrationId;
+				break;
+			}
+		}
+
+		if (!empty($latestMigration))
+			// Rollback the latest migrated migration.
+			return $this->rollbackOne($latestMigration);
+		else
+			// No latest migration, do nothing and return NULL.
+			return null;
+	}
+
+	/**
+	 * The preparations clear scripts filename regex.
+	 */
+	const string PREPARATIONS_CLEAR_SCRIPT_REGEX = "/^0+_(.*)$/";
+
+	/**
+	 * Clear database preparations.
+	 * Database preparations are cleared before migrations and should drop all functions and views used by tables that can
+	 * be changed by migrations.
+	 * @return void
+	 */
+	public function clearPreparations(): void
+	{
+		foreach ($this->preparations as $preparationScript)
+		{ // Execute all preparations clear scripts.
+			if (preg_match(static::PREPARATIONS_CLEAR_SCRIPT_REGEX, $preparationScript))
+				// Only execute files with 00_ prefix.
+				$this->execPreparation($preparationScript);
+		}
+	}
+
+	/**
+	 * Do database preparations.
+	 * Database preparations are executed after migrations and can create functions and views based on tables.
+	 * @return void
+	 */
+	public function prepare(): void
+	{
+		foreach ($this->preparations as $preparationScript)
+		{ // Execute all preparations that are not clear scripts.
+			if (!preg_match(static::PREPARATIONS_CLEAR_SCRIPT_REGEX, $preparationScript))
+				// Only execute files that aren't preparations clear scripts.
+				$this->execPreparation($preparationScript);
+		}
+	}
+
+	/**
+	 * Execute a given preparation script.
+	 * @param string $preparationScript The preparation script to execute.
+	 * @return void
+	 */
+	private function execPreparation(string $preparationScript): void
+	{
+		// Read preparation script and execute it.
+		$this->database->execute(file_get_contents($preparationScript));
+	}
+}
diff --git a/src/Migrations/MigrationsService.php b/src/Migrations/MigrationsService.php
new file mode 100644
index 0000000..a61dcb8
--- /dev/null
+++ b/src/Migrations/MigrationsService.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace Nest\Database\Migrations;
+
+use Nest\Database\Migrations\Configuration\MigrationsConfiguration;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+use Nest\Database\Exceptions\UnknownDatabaseException;
+use Nest\Exceptions\Services\Configuration\UndefinedServiceConfigurationException;
+use Nest\Types\Exceptions\IncompatibleTypeException;
+
+/**
+ * Nest database migrations service.
+ */
+trait MigrationsService
+{
+	/**
+	 * The database migrations instance.
+	 * @var Migrations
+	 */
+	private Migrations $migrations;
+
+	/**
+	 * @throws UndefinedServiceConfigurationException
+	 * @throws UnknownDatabaseException
+	 * @throws MissingConditionValueException
+	 * @throws IncompatibleTypeException
+	 */
+	protected function __nest__MigrationsService(): void
+	{
+		// Initialize database migrations instance.
+		$this->migrations = new Migrations($this, $this->getServiceConfiguration(MigrationsConfiguration::class));
+	}
+
+	/**
+	 * Database migrations service.
+	 * @return Migrations The database migrations manager.
+	 */
+	public function migrations(): Migrations
+	{
+		return $this->migrations;
+	}
+}
diff --git a/src/Migrations/Model/Migration.php b/src/Migrations/Model/Migration.php
new file mode 100644
index 0000000..76302bf
--- /dev/null
+++ b/src/Migrations/Model/Migration.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Nest\Database\Migrations\Model;
+
+use Carbon\Carbon;
+use Nest\Model\Entity;
+use Nest\Model\EntityBlueprint;
+use Nest\Types\Definitions\StringType;
+
+/**
+ * Class of an executed migration.
+ */
+class Migration extends Entity
+{
+	/**
+	 * Migration version ID.
+	 * @var string
+	 */
+	public string $id;
+
+	/**
+	 * Migration name.
+	 * @var string
+	 */
+	public string $name;
+
+	/**
+	 * Migration execution date.
+	 * @var Carbon
+	 */
+	public Carbon $created_at;
+
+	/**
+	 * @inheritDoc
+	 */
+	public function definition(EntityBlueprint $blueprint): EntityBlueprint
+	{
+		$blueprint->field("id", StringType::class)->primary();
+		$blueprint->field("name", StringType::class)->index();
+		$blueprint->createdAt();
+
+		return $blueprint;
+	}
+}
diff --git a/src/PdoDatabase.php b/src/PdoDatabase.php
new file mode 100644
index 0000000..465f9c0
--- /dev/null
+++ b/src/PdoDatabase.php
@@ -0,0 +1,111 @@
+<?php
+
+namespace Nest\Database;
+
+use Nest\Database\Events\PdoDatabaseAfterConnectionEvent;
+use Nest\Database\Events\PdoDatabaseBeforeConnectionEvent;
+use Nest\Events\HasEvents;
+use PDO;
+
+/**
+ * Class of a PDO database.
+ */
+abstract class PdoDatabase extends Database
+{
+	use HasEvents;
+
+	/**
+	 * The PDO connection to database.
+	 * @var PDO
+	 */
+	protected PDO $pdo;
+
+	/**
+	 * @return string The PDO DSN to connect to the database.
+	 */
+	protected abstract function getDsn(): string;
+
+	/**
+	 * @return string The username to connect to the database.
+	 */
+	protected abstract function getUsername(): string;
+
+	/**
+	 * @return string The password to connect to the database.
+	 */
+	protected abstract function getPassword(): string;
+
+	/**
+	 * @return array PDO options.
+	 * @see PDO::__construct
+	 */
+	protected function getPdoOptions(): array
+	{
+		return [
+			// Persistent connection by default.
+			PDO::ATTR_PERSISTENT => true,
+			PDO::ERRMODE_EXCEPTION => true,
+		];
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function connect(): void
+	{
+		$this->getEventsManager()->fire(new PdoDatabaseBeforeConnectionEvent($this));
+
+		// Connect to the database using PDO.
+		$this->pdo = new PDO($this->getDsn(), $this->getUsername(), $this->getPassword(), $this->getPdoOptions());
+
+		$this->getEventsManager()->fire(new PdoDatabaseAfterConnectionEvent($this, $this->pdo));
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function execute(string $statement, array $bindings = []): array
+	{
+		// Prepare the statement.
+		$statement = $this->getConnection()->prepare($statement);
+		foreach ($bindings as $param => $value)
+		{ // Assign bindings to the statement.
+			$statement->bindValue(is_int($param) ? $param + 1 : $param, $value);
+		}
+
+		// Exception is thrown in case of failure.
+		$statement->execute();
+
+		// Fetching results.
+		$result = [];
+		while ($obj = $statement->fetchObject())
+		{ // Fetch next object while there is one.
+			$result[] = $obj;
+		}
+
+		// Return results.
+		return $result;
+	}
+
+	/**
+	 * Check if the connection to the database is active.
+	 * @return bool True if the connection to the database is active, false otherwise.
+	 */
+	public function isConnected(): bool
+	{
+		return !empty($this->pdo);
+	}
+
+	/**
+	 * Get the current connection to the database.
+	 * @return PDO
+	 */
+	public function getConnection(): PDO
+	{
+		if (!$this->isConnected())
+			// If we are not connected, trying to connect to the database.
+			$this->connect();
+
+		return $this->pdo;
+	}
+}
diff --git a/src/PostgreSql/Columns/Bit.php b/src/PostgreSql/Columns/Bit.php
new file mode 100644
index 0000000..f229db7
--- /dev/null
+++ b/src/PostgreSql/Columns/Bit.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL fixed-length bit string column type.
+ */
+class Bit implements Stringable
+{
+	/**
+	 * @param int $size Size of the fixed-length bit string column type.
+	 */
+	public function __construct(protected int $size)
+	{}
+
+	public function __toString(): string
+	{
+		return "bit($this->size)";
+	}
+}
diff --git a/src/PostgreSql/Columns/Char.php b/src/PostgreSql/Columns/Char.php
new file mode 100644
index 0000000..1b6115e
--- /dev/null
+++ b/src/PostgreSql/Columns/Char.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL fixed-length character string column type.
+ */
+class Char implements Stringable
+{
+	/**
+	 * @param int $size Size of the fixed-length character string column type.
+	 */
+	public function __construct(protected int $size)
+	{}
+
+	public function __toString(): string
+	{
+		return "char($this->size)";
+	}
+}
diff --git a/src/PostgreSql/Columns/Numeric.php b/src/PostgreSql/Columns/Numeric.php
new file mode 100644
index 0000000..917c1da
--- /dev/null
+++ b/src/PostgreSql/Columns/Numeric.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL numeric column type.
+ */
+class Numeric implements Stringable
+{
+	/**
+	 * @param int $precision Precision of the numeric column type.
+	 * @param int $scale Scale of the numeric column type.
+	 * @see https://www.postgresql.org/docs/current/datatype-numeric.html#DATATYPE-NUMERIC-DECIMAL
+	 */
+	public function __construct(protected int $precision, protected int $scale = 0)
+	{}
+
+	public function __toString(): string
+	{
+		return "numeric($this->precision, $this->scale)";
+	}
+}
diff --git a/src/PostgreSql/Columns/Time.php b/src/PostgreSql/Columns/Time.php
new file mode 100644
index 0000000..1fa9d58
--- /dev/null
+++ b/src/PostgreSql/Columns/Time.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL time column type.
+ */
+class Time implements Stringable
+{
+	/**
+	 * @param bool $timezone Add timezone to the value.
+	 */
+	public function __construct(protected bool $timezone = false)
+	{}
+
+	public function __toString(): string
+	{
+		return "time" . ($this->timezone ? " with time zone" : "");
+	}
+}
diff --git a/src/PostgreSql/Columns/Timestamp.php b/src/PostgreSql/Columns/Timestamp.php
new file mode 100644
index 0000000..073ba3f
--- /dev/null
+++ b/src/PostgreSql/Columns/Timestamp.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL date + time column type.
+ */
+class Timestamp implements Stringable
+{
+	/**
+	 * @param bool $timezone Add timezone to the value.
+	 */
+	public function __construct(protected bool $timezone = false)
+	{}
+
+	public function __toString(): string
+	{
+		return "timestamp" . ($this->timezone ? " with time zone" : "");
+	}
+}
diff --git a/src/PostgreSql/Columns/Type.php b/src/PostgreSql/Columns/Type.php
new file mode 100644
index 0000000..2041bb7
--- /dev/null
+++ b/src/PostgreSql/Columns/Type.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+/**
+ * PostgreSQL simple column types.
+ * See also parametric types:
+ * @see Bit
+ * @see Varbit
+ * @see Char
+ * @see Varchar
+ * @see Numeric
+ */
+enum Type: string
+{
+	case Boolean = "boolean";
+
+	case SmallInt = "smallint";
+	case SmallSerial = "smallserial";
+	case Int = "int";
+	case Serial = "serial";
+	case BigInt = "bigint";
+	case BigSerial = "bigserial";
+
+	case Float = "float4";
+	case Double = "float8";
+	case Numeric = "numeric";
+	case Money = "money";
+
+	case Bit = "bit";
+	case Varbit = "varbit";
+	case ByteArray = "bytea";
+
+	case Char = "char";
+	case Varchar = "varchar";
+	case Text = "text";
+	case TextSearchQuery = "tsquery";
+	case TextSearchVector = "tsvector";
+
+	case Uuid = "uuid";
+
+	case Json = "json";
+	case JsonBinary = "jsonb";
+	case Xml = "xml";
+
+	case Date = "date";
+	case Time = "time";
+	case Timestamp = "timestamp";
+	case Interval = "interval";
+
+	case Cidr = "cidr";
+	case MacAddr = "macaddr";
+	case MacAddr8 = "macaddr8";
+
+	case Point = "point";
+	case Line = "line";
+	case Segment = "lseg";
+	case Path = "path";
+	case Polygon = "polygon";
+	case Box = "box";
+	case Circle = "circle";
+}
diff --git a/src/PostgreSql/Columns/Varbit.php b/src/PostgreSql/Columns/Varbit.php
new file mode 100644
index 0000000..61ffb05
--- /dev/null
+++ b/src/PostgreSql/Columns/Varbit.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL variable-length bit string column type.
+ */
+class Varbit implements Stringable
+{
+	/**
+	 * @param int $size Size of the variable-length bit string column type.
+	 */
+	public function __construct(protected int $size)
+	{}
+
+	public function __toString(): string
+	{
+		return "varbit($this->size)";
+	}
+}
diff --git a/src/PostgreSql/Columns/Varchar.php b/src/PostgreSql/Columns/Varchar.php
new file mode 100644
index 0000000..971c726
--- /dev/null
+++ b/src/PostgreSql/Columns/Varchar.php
@@ -0,0 +1,22 @@
+<?php
+
+namespace Nest\Database\PostgreSql\Columns;
+
+use Stringable;
+
+/**
+ * PostgreSQL variable-length character string column type.
+ */
+class Varchar implements Stringable
+{
+	/**
+	 * @param int $size Size of the variable-length character string column type.
+	 */
+	public function __construct(protected int $size)
+	{}
+
+	public function __toString(): string
+	{
+		return "varchar($this->size)";
+	}
+}
diff --git a/src/PostgreSql/PostgreSql.php b/src/PostgreSql/PostgreSql.php
new file mode 100644
index 0000000..e9da756
--- /dev/null
+++ b/src/PostgreSql/PostgreSql.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Database\PostgreSql;
+
+use Nest\Database\Configuration\DatabaseFactory;
+use Nest\Database\Database;
+
+class PostgreSql extends DatabaseFactory
+{
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function make(): Database
+	{
+		return new PostgreSqlDatabase(
+			$this->getRequiredConfig("host"),
+			$this->getRequiredConfig("database"),
+			$this->getRequiredConfig("username"),
+			$this->getRequiredConfig("password"),
+			$this->getOptionalConfig("port", 5432),
+		);
+	}
+}
diff --git a/src/PostgreSql/PostgreSqlAdapter.php b/src/PostgreSql/PostgreSqlAdapter.php
new file mode 100644
index 0000000..4fada0b
--- /dev/null
+++ b/src/PostgreSql/PostgreSqlAdapter.php
@@ -0,0 +1,501 @@
+<?php
+
+namespace Nest\Database\PostgreSql;
+
+use Nest\Database\DatabaseAdapter;
+use Nest\Database\Migrations\Diff\TableColumn;
+use Nest\Database\Migrations\Diff\TableForeignKey;
+use Nest\Database\Migrations\Diff\TableIndex;
+use Nest\Database\Query\Join\JoinBuilder;
+use Nest\Database\Query\Raw;
+use Nest\Database\Query\Where\ConditionBuilder;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+use Override;
+use function Nest\Database\Utils\format_object_name;
+
+/**
+ * PostgreSQL database queries adapter.
+ */
+class PostgreSqlAdapter extends DatabaseAdapter
+{
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function newTransaction(): void
+	{
+		$this->database->execute("BEGIN;");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function rollbackTransaction(): void
+	{
+		$this->database->execute("ROLLBACK;");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function commitTransaction(): void
+	{
+		$this->database->execute("COMMIT;");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[Override] public function createTable(string $tableName, bool $ifNotExists = false): void
+	{
+		$this->database->execute("CREATE TABLE ".($ifNotExists ? "IF NOT EXISTS " : "").format_object_name($tableName)."();");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function dropTable(string $tableName, bool $ifExists = false): void
+	{
+		$this->database->execute("DROP TABLE ".($ifExists ? "IF EXISTS " : "").format_object_name($tableName).";");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function renameTable(string $tableName, string $newTableName): void
+	{
+		$this->database->execute("ALTER TABLE ".format_object_name($tableName)." RENAME TO ".format_object_name($newTableName).";");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function addTableColumn(TableColumn $tableColumn, bool $ifNotExists = false): void
+	{
+		// SQL base query.
+		$sql = "ADD COLUMN".($ifNotExists ? " IF NOT EXISTS" : "")." ".format_object_name($tableColumn->name)." $tableColumn->type";
+
+		// Set nullable or not.
+		if (!empty($tableColumn->nullable))
+			$sql .= " NULL";
+		else
+			$sql .= " NOT NULL";
+
+		// Set default value if there is one.
+		if (isset($tableColumn->default))
+			$sql .= " DEFAULT ".((string) $tableColumn->default);
+
+		if (!empty($tableColumn->primary))
+			$sql .= " PRIMARY KEY";
+
+		// Execute add table column.
+		$this->database->execute("ALTER TABLE ".format_object_name($tableColumn->table->getTableName())." {$sql};");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function setTableColumnIndex(TableColumn $tableColumn): void
+	{
+		// Create index name.
+		$indexName = $tableColumn->table->getTableName()."_".$tableColumn->name."_index";
+
+		// Drop existing index, if it exists.
+		$this->database->execute("DROP INDEX IF EXISTS {$indexName};");
+
+		// SQL base query.
+		$sql = "CREATE ".($tableColumn->index->unique ? "UNIQUE " : "")."INDEX $indexName ON ".format_object_name($tableColumn->table->getTableName());
+
+		// Set index method if specified.
+		if (!empty($tableColumn->index->method))
+			$sql .= " USING ({$tableColumn->index->method})";
+
+		// Set column name in new index.
+		$sql .= " ({$tableColumn->name})";
+
+		// Execute add column index.
+		$this->database->execute("$sql;");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function renameTableColumn(TableColumn $tableColumn, string $newName): void
+	{
+		$this->database->execute("ALTER TABLE ".format_object_name($tableColumn->table->getTableName()).
+			" RENAME COLUMN ".format_object_name($tableColumn->name).
+			" TO ".format_object_name($newName));
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function alterTableColumn(TableColumn $tableColumn): void
+	{
+		// SQL base query.
+		$sql = "ALTER COLUMN ".format_object_name($tableColumn->name);
+
+		if (!empty($tableColumn->type))
+			$sql .= " TYPE $tableColumn->type";
+
+		// Set nullable or not.
+		if (isset($tableColumn->nullable))
+		{
+			if ($tableColumn->nullable)
+				$sql .= " DROP NOT NULL";
+			else
+				$sql .= " SET NOT NULL";
+		}
+
+		// Set default value if there is one.
+		if (isset($tableColumn->default))
+			$sql .= " SET DEFAULT ".((string) $tableColumn->default);
+
+		// Execute add table column.
+		$this->database->execute("ALTER TABLE ".format_object_name($tableColumn->table->getTableName())." {$sql};");
+
+		if (!empty($tableColumn->primary))
+			// Set the column as a primary key.
+			$this->database->execute("ALTER TABLE ".format_object_name($tableColumn->table->getTableName())." ADD PRIMARY KEY (".format_object_name($tableColumn->name).");");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function dropTableColumn(string $tableName, string $columnName, bool $ifExists = false): void
+	{
+		// SQL base query.
+		$sql = "DROP COLUMN ".($ifExists ? "IF EXISTS " : "").format_object_name($columnName);
+
+		// Execute drop table column.
+		$this->database->execute("ALTER TABLE ".format_object_name($tableName)." {$sql};");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function dropConstraint(string $tableName, string $constraintName, bool $ifExists = false): void
+	{
+		// SQL base query.
+		$sql = "DROP CONSTRAINT ".($ifExists ? "IF EXISTS " : "").format_object_name($constraintName);
+
+		// Execute drop table constraint.
+		$this->database->execute("ALTER TABLE ".format_object_name($tableName)." {$sql};");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function createForeignKey(TableForeignKey $foreignKey): void
+	{
+		// Format columns list.
+		$columns = implode(", ", array_map(fn ($column) => format_object_name($column), $foreignKey->columns));
+
+		// Format referenced columns list.
+		$referencedColumns = implode(", ", array_map(fn ($column) => format_object_name($column), $foreignKey->referencedColumns));
+
+		// Base SQL.
+		$sql = "ADD FOREIGN KEY ($columns) REFERENCES ".format_object_name($foreignKey->referencedTable)."($referencedColumns)";
+
+		// Set ON DELETE and ON UPDATE actions.
+		if (!empty($foreignKey->onDelete))
+			$sql .= " ON DELETE {$foreignKey->onDelete}";
+		if (!empty($foreignKey->onUpdate))
+			$sql .= " ON UPDATE {$foreignKey->onUpdate}";
+
+		// Execute add foreign key constraint.
+		$this->database->execute("ALTER TABLE ".format_object_name($foreignKey->table->getTableName())." {$sql};");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function createIndex(TableIndex $index, bool $ifNotExists = false): void
+	{
+		// Base SQL.
+		$sql = "CREATE (UNIQUE) INDEX".($ifNotExists ? " IF NOT EXISTS" : "")." $index->name ON ".format_object_name($index->table->getTableName());
+
+		if (!empty($index->method))
+			$sql .= " USING $index->method";
+
+		$sql .= "(";
+
+		if (!empty($index->rawExpression))
+			$sql .= "($index->rawExpression)";
+		else
+		{ // Format indexed columns.
+			// Format columns list.
+			$columns = implode(", ", array_map(fn ($column) => format_object_name($column), $index->columns));
+			$sql .= "($columns)";
+		}
+
+		// Set index order, if defined.
+		if (!empty($index->order))
+			$sql .= " $index->order";
+		if (!empty($index->nulls))
+			$sql .= " $index->nulls";
+
+		$sql .= ")";
+
+		// Execute index creation.
+		$this->database->execute("$sql;");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function renameIndex(string $indexName, string $newName, bool $ifExists = false): void
+	{
+		// Execute index rename.
+		$this->database->execute("ALTER INDEX".($ifExists ? "IF EXISTS " : "")." ".format_object_name($indexName).
+			" RENAME TO ".format_object_name($newName).";");
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function dropIndex(TableIndex $index, bool $ifExists = false): void
+	{
+		// Execute index drop.
+		$this->database->execute("DROP INDEX".($ifExists ? "IF EXISTS " : "")." ".format_object_name($index->name).";");
+	}
+
+	/**
+	 * Build JOIN clauses from join builders.
+	 * @param JoinBuilder[] $joins Joins to build.
+	 * @return array{string, array} The built SQL with its bindings, if there are some. Bindings can be empty or non-existent.
+	 * @throws MissingConditionValueException
+	 */
+	protected function buildJoins(array $joins): array
+	{
+		// Return empty join clauses if there are no conditions.
+		if (empty($joins)) return ["", []];
+
+		$sql = "";
+		$bindings = [];
+
+		// Build all join clauses.
+		foreach ($joins as $join)
+		{ // For each join clause, build its conditions and append the built bindings.
+			[$onSql, $onBindings] = $this->buildWhere($join->getConditions(), "ON");
+			$sql .= "$join->type JOIN \"$join->table\" $onSql ";
+			array_push($bindings, ...$onBindings);
+		}
+
+		// Return all joins clauses SQL and bindings.
+		return [$sql, $bindings];
+	}
+
+	/**
+	 * Build WHERE clause from conditions builders.
+	 * @param ConditionBuilder[] $wheres Conditions to build.
+	 * @param string $keyword The keyword to use. "WHERE" by default, but can be replaced by "ON" for JOIN conditions.
+	 * @return array{string, array} The built SQL with its bindings, if there are some. Bindings can be empty or non-existent.
+	 * @throws MissingConditionValueException
+	 */
+	protected function buildWhere(array $wheres, string $keyword = "WHERE"): array
+	{
+		// Return empty where clause if there are no conditions.
+		if (empty($wheres)) return ["", []];
+
+		// Build all conditions.
+		$conditions = array_map(fn (ConditionBuilder $condition) => $condition->toSql(), $wheres);
+		// Join all conditions with AND.
+		$sql = implode("AND", array_column($conditions, 0));
+		// Join all values bindings.
+		$bindings = array_merge(...array_column($conditions, 1));
+
+		// Return built WHERE clause.
+		return ["$keyword $sql", $bindings];
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function buildSelect(string $tableName, array $selected, array $joins, array $wheres, ?int $limit = null): Raw
+	{
+		$bindings = []; // Initialize empty bindings.
+
+		// SQL base query: select the table columns.
+		$sql = "SELECT ".implode(", ", array_map(function (Raw|string|array $select) use (&$bindings) {
+			if ($select instanceof Raw)
+			{ // Raw selection.
+				// Add its bindings to the list.
+				array_push($bindings, ...$select->bindings);
+				// Return raw SQL.
+				return (string) $select;
+			}
+			else
+				// Format selection and return its SQL.
+				return format_object_name((string) $select);
+		}, $selected));
+
+		// Append FROM clause.
+		$sql .= " FROM ".format_object_name($tableName);
+
+		// Append JOIN clauses.
+		[$joinsSql, $joinsBindings] = $this->buildJoins($joins);
+		if (!empty($joinsSql))
+		{
+			$sql .= " $joinsSql";
+			array_push($bindings, ...$joinsBindings);
+		}
+
+		// Append WHERE clause.
+		[$whereSql, $whereBindings] = $this->buildWhere($wheres);
+		if (!empty($whereSql))
+		{
+			$sql .= " $whereSql";
+			array_push($bindings, ...$whereBindings);
+		}
+
+		// Append LIMIT clause.
+		if (!is_null($limit))
+			$sql .= " LIMIT $limit";
+
+		// Return raw SQL with its bindings.
+		return new Raw($sql, $bindings);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function select(string $tableName, array $selected, array $joins, array $wheres, ?int $limit = null): array
+	{
+		// Build SELECT query.
+		$raw = $this->buildSelect($tableName, $selected, $joins, $wheres, $limit);
+
+		// Execute built query and return result.
+		return $this->database->execute($raw->sql, $raw->bindings);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function insert(string $tableName, array $columns, array $rows, bool $returning = false): array|bool
+	{
+		// SQL base query: insert into the table columns.
+		$sql = "INSERT INTO ".format_object_name($tableName).
+			" (".implode(", ", array_map(fn (string $column) => format_object_name($column), $columns)).")";
+
+		// Add values (with bindings).
+		$sql .= " VALUES ";
+		$rowsValues = [];
+		$bindings = [];
+		foreach ($rows as $row)
+		{ // Create a new VALUES tuple for each row.
+			// Initialize row parts of the current row.
+			$rowParts = [];
+			$rowBindings = [];
+
+			foreach ($row as $value)
+			{ // For each row value, add a row part corresponding to its type.
+				if ($value instanceof Raw)
+					// Add a new raw row part.
+					$rowParts[] = (string) $value;
+				else
+				{ // Add a new row part, with its binding.
+					$rowParts[] = "?";
+					$rowBindings[] = $value;
+				}
+			}
+
+			// Append current row tuple to values, with its bindings.
+			$rowsValues[] = "(".implode(", ", $rowParts).")";
+			array_push($bindings, ...$rowBindings);
+		}
+
+		// Build values SQL and append it to the query.
+		$sql .= implode(", ", $rowsValues);
+
+		if ($returning)
+			// Inserted rows shall be returned, indicating it in the query.
+			$sql .= "RETURNING *";
+
+		// SQL query end.
+		$sql .= ";";
+
+		// Execute INSERT query.
+		$result = $this->database->execute($sql, $bindings);
+
+		if ($returning)
+			// Returning inserted rows.
+			return $result;
+		else
+			// INSERT executed successfully.
+			return true;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function update(string $tableName, array $set, array $wheres, bool $returning = false): array|bool
+	{
+		// SQL base query: update the given table.
+		$sql = "UPDATE ".format_object_name($tableName);
+		$bindings = []; // Initialize empty bindings.
+
+		// Initialize SET clause.
+		$sql .= " SET ";
+		$setParts = [];
+		foreach ($set as $columnName => $value)
+		{ // For each set value, add a set part corresponding to its type.
+			$currentSet = format_object_name($columnName)." = ";
+			if ($value instanceof Raw)
+				// Add a new raw set part.
+				$setParts[] = $currentSet.((string) $value);
+			else
+			{ // Add a new set part, with its binding.
+				$setParts[] = $currentSet."?";
+				$bindings[] = $value;
+			}
+		}
+
+		// Append SET columns.
+		$sql .= implode(", ", $setParts);
+
+		// Append WHERE clause.
+		[$whereSql, $whereBindings] = $this->buildWhere($wheres);
+		if (!empty($whereSql))
+		{
+			$sql .= " $whereSql";
+			array_push($bindings, ...$whereBindings);
+		}
+
+		if ($returning)
+			// Inserted rows shall be returned, indicating it in the query.
+			$sql .= "RETURNING *";
+
+		// SQL query end.
+		$sql .= ";";
+
+		// Execute UPDATE query.
+		$result = $this->database->execute($sql, $bindings);
+
+		if ($returning)
+			// Returning updated rows.
+			return $result;
+		else
+			// UPDATE executed successfully.
+			return true;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function delete(string $tableName, array $wheres): void
+	{
+		// SQL base query: delete from the given table.
+		$sql = "DELETE FROM ".format_object_name($tableName);
+
+		// Append WHERE clause.
+		[$whereSql, $bindings] = $this->buildWhere($wheres);
+		if (!empty($whereSql))
+			$sql .= " $whereSql";
+
+		// SQL query end.
+		$sql .= ";";
+
+		// Execute DELETE query.
+		$this->database->execute($sql, $bindings);
+	}
+}
diff --git a/src/PostgreSql/PostgreSqlDatabase.php b/src/PostgreSql/PostgreSqlDatabase.php
new file mode 100644
index 0000000..8808a70
--- /dev/null
+++ b/src/PostgreSql/PostgreSqlDatabase.php
@@ -0,0 +1,51 @@
+<?php
+
+namespace Nest\Database\PostgreSql;
+
+use Nest\Database\DatabaseAdapter;
+use Nest\Database\PdoDatabase;
+
+class PostgreSqlDatabase extends PdoDatabase
+{
+	/**
+	 * @param string $host Database host or unix socket directory path.
+	 * @param string $database Database name.
+	 * @param string $username Username to use to connect to the database.
+	 * @param string $password Password to use to connect to the database.
+	 * @param int $port Database port.
+	 */
+	public function __construct(protected string $host, protected string $database, protected string $username, protected string $password, protected int $port = 5432)
+	{}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] public function getQueriesAdapter(): DatabaseAdapter
+	{
+		return new PostgreSqlAdapter($this);
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] protected function getDsn(): string
+	{
+		return "pgsql:host={$this->host};port={$this->port};dbname={$this->database}";
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] protected function getUsername(): string
+	{
+		return $this->username;
+	}
+
+	/**
+	 * @inheritDoc
+	 */
+	#[\Override] protected function getPassword(): string
+	{
+		return $this->password;
+	}
+}
diff --git a/src/Query/DeleteQuery.php b/src/Query/DeleteQuery.php
new file mode 100644
index 0000000..027baa7
--- /dev/null
+++ b/src/Query/DeleteQuery.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Nest\Database\Query;
+
+use Nest\Database\Database;
+use Nest\Database\Query\Where\HasWhere;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+
+/**
+ * Builder of a DELETE query.
+ */
+class DeleteQuery
+{
+	use HasWhere;
+
+	/**
+	 * Create a new DELETE query.
+	 * @param Database $database The database on which to execute the query.
+	 * @param string $table Base table of the DELETE query.
+	 */
+	public function __construct(protected Database $database, protected string $table)
+	{}
+
+	/**
+	 * Get the database on which to execute the query.
+	 * @return Database
+	 */
+	public function getDatabase(): Database
+	{
+		return $this->database;
+	}
+
+	/**
+	 * Execute DELETE query.
+	 * @return void
+	 * @throws MissingConditionValueException
+	 */
+	public function execute(): void
+	{
+		// Execute built query and return result.
+		$this->database->getQueriesAdapter()->delete($this->table, $this->wheres);
+	}
+}
diff --git a/src/Query/InsertQuery.php b/src/Query/InsertQuery.php
new file mode 100644
index 0000000..f12eeb6
--- /dev/null
+++ b/src/Query/InsertQuery.php
@@ -0,0 +1,75 @@
+<?php
+
+namespace Nest\Database\Query;
+
+use Nest\Database\Database;
+use function Nest\Utils\array_unique_quick;
+
+/**
+ * Builder of an INSERT query.
+ */
+class InsertQuery
+{
+	/**
+	 * Values to insert.
+	 * @var array<array<string, Raw|string|int|float|null>>
+	 */
+	protected array $values = [];
+
+	/**
+	 * Create a new INSERT query.
+	 * @param Database $database The database on which to execute the query.
+	 * @param string $table Base table of the INSERT query.
+	 */
+	public function __construct(protected Database $database, protected string $table)
+	{}
+
+	/**
+	 * Reset values to insert.
+	 * @return $this
+	 */
+	public function resetValues(): static
+	{
+		$this->values = [];
+		return $this;
+	}
+
+	/**
+	 * Add values to insert.
+	 * @param array<string, Raw|string|int|float|null> ...$row Each parameter is an associative array that represents one row data.
+	 * @return $this
+	 */
+	public function values(array ...$row): static
+	{
+		// Append all rows to values array.
+		array_push($this->values, ...$row);
+		return $this;
+	}
+
+	/**
+	 * Execute insert query.
+	 * @param bool $returning True to return inserted objects.
+	 * @return object[]|bool Inserted objects if returning is true, true otherwise.
+	 */
+	public function execute(bool $returning = false): array|bool
+	{
+		// Find all inserted columns.
+		$columns = array_unique_quick(array_merge(...array_map(fn (array $row) => array_keys($row), $this->values)));
+
+		// Prepare rows to insert (fill rows with DEFAULT values, if some of them are missing something).
+		$rows = array_map(function (array $rowValues) use ($columns) {
+			// Initialize current row.
+			$row = [];
+
+			foreach ($columns as $column)
+			{ // Get value for each column: from row values if it is defined, use DEFAULT otherwise.
+				$row[$column] = $rowValues[$column] ?? new Raw("DEFAULT");
+			}
+
+			return $row; // Return full row ready to insert.
+		}, $this->values);
+
+		// Perform insert.
+		return $this->database->getQueriesAdapter()->insert($this->table, $columns, $rows, $returning);
+	}
+}
diff --git a/src/Query/Join/HasJoin.php b/src/Query/Join/HasJoin.php
new file mode 100644
index 0000000..d6162ef
--- /dev/null
+++ b/src/Query/Join/HasJoin.php
@@ -0,0 +1,78 @@
+<?php
+
+namespace Nest\Database\Query\Join;
+
+/**
+ * Add join capacity to a query builder.
+ */
+trait HasJoin
+{
+	/**
+	 * Join clauses.
+	 * @var JoinBuilder[]
+	 */
+	protected array $joins = [];
+
+	/**
+	 * Reset JOIN clauses.
+	 * @return $this
+	 */
+	public function resetJoins(): static
+	{
+		$this->joins = [];
+		return $this;
+	}
+
+	/**
+	 * Create a new join clause.
+	 * @param string $type Type of the join clause.
+	 * @param string $table Joined table.
+	 * @return JoinBuilder New join clause builder.
+	 */
+	public function join(string $type, string $table): JoinBuilder
+	{
+		$join = new JoinBuilder($this, $type, $table);
+		$this->joins[] = $join;
+		return $join;
+	}
+
+	/**
+	 * Create a new inner join clause.
+	 * @param string $table Joined table.
+	 * @return JoinBuilder New join clause builder.
+	 */
+	public function innerJoin(string $table): JoinBuilder
+	{
+		return $this->join(JoinBuilder::INNER, $table);
+	}
+
+	/**
+	 * Create a new outer join clause.
+	 * @param string $table Joined table.
+	 * @return JoinBuilder New join clause builder.
+	 */
+	public function outerJoin(string $table): JoinBuilder
+	{
+		return $this->join(JoinBuilder::OUTER, $table);
+	}
+
+	/**
+	 * Create a new left join clause.
+	 * @param string $table Joined table.
+	 * @return JoinBuilder New join clause builder.
+	 */
+	public function leftJoin(string $table): JoinBuilder
+	{
+		return $this->join(JoinBuilder::LEFT, $table);
+	}
+
+	/**
+	 * Create a new right join clause.
+	 * @param string $table Joined table.
+	 * @return JoinBuilder New join clause builder.
+	 */
+	public function rightJoin(string $table): JoinBuilder
+	{
+		return $this->join(JoinBuilder::RIGHT, $table);
+	}
+}
diff --git a/src/Query/Join/JoinBuilder.php b/src/Query/Join/JoinBuilder.php
new file mode 100644
index 0000000..8965a0f
--- /dev/null
+++ b/src/Query/Join/JoinBuilder.php
@@ -0,0 +1,75 @@
+<?php
+
+namespace Nest\Database\Query\Join;
+
+use Nest\Database\Query\Where\ConditionBuilder;
+
+class JoinBuilder
+{
+	const string INNER = "INNER";
+	const string OUTER = "OUTER";
+	const string LEFT = "LEFT";
+	const string RIGHT = "RIGHT";
+
+	/**
+	 * @param mixed $query The calling query.
+	 * @param string $type Join type (INNER, OUTER, LEFT, RIGHT, ...).
+	 * @param string $table The table to join.
+	 */
+	public function __construct(protected mixed $query, public readonly string $type, public readonly string $table)
+	{}
+
+	/**
+	 * ON conditions of the JOIN clause.
+	 * @var ConditionBuilder[]
+	 */
+	protected array $on = [];
+
+	/**
+	 * Reset ON conditions.
+	 * @return $this
+	 */
+	public function resetOn(): static
+	{
+		$this->on = [];
+		return $this;
+	}
+
+	/**
+	 * Add a ON condition.
+	 * @param string|callable $column The column of the condition, or a condition builder callable.
+	 * @param string $operator The operator of the condition (or the value column if no value is passed).
+	 * @param string|null $valueColumn The value column of the condition.
+	 * @return mixed The query.
+	 */
+	public function on(string|callable $column, string $operator, string $valueColumn = null): mixed
+	{
+		if (is_callable($column))
+		{ // Callable condition builder.
+			$this->on[] = $column(new ConditionBuilder());
+		}
+		else
+		{ // Simple condition, registering it.
+			if (!empty($operator) && empty($valueColumn))
+			{ // If there are 2 parameters, considering the second one as the value, with default operator.
+				$valueColumn = $operator;
+				// Default operator: "=".
+				$operator = "=";
+			}
+
+			// Create the simple condition.
+			$this->on[] = (new ConditionBuilder())->column($column)->operator($operator)->column($valueColumn);
+		}
+
+		return $this->query;
+	}
+
+	/**
+	 * Get join conditions.
+	 * @return ConditionBuilder[] ON conditions of the JOIN clause.
+	 */
+	public function getConditions(): array
+	{
+		return $this->on;
+	}
+}
diff --git a/src/Query/QueryBuilder.php b/src/Query/QueryBuilder.php
new file mode 100644
index 0000000..6bdab6a
--- /dev/null
+++ b/src/Query/QueryBuilder.php
@@ -0,0 +1,92 @@
+<?php
+
+namespace Nest\Database\Query;
+
+use Nest\Database\Database;
+
+/**
+ * Database query builder.
+ */
+class QueryBuilder
+{
+	/**
+	 * Base table of the query.
+	 * @var string
+	 */
+	protected string $table;
+
+	/**
+	 * Build a new query builder.
+	 * @param Database $database The database on which to execute the query.
+	 * @param string|null $table Base table of the query.
+	 */
+	public function __construct(protected Database $database, ?string $table = null)
+	{
+		if (!empty($table)) $this->setTable($table);
+	}
+
+	/**
+	 * Get the database on which to execute the query.
+	 * @return Database
+	 */
+	public function getDatabase(): Database
+	{
+		return $this->database;
+	}
+
+	/**
+	 * Set the table to use in the query.
+	 * @param string $table The table to use in the query.
+	 * @return $this
+	 */
+	public function setTable(string $table): static
+	{
+		$this->table = $table;
+		return $this;
+	}
+
+	/**
+	 * Get the table to use in the query.
+	 * @return string
+	 */
+	public function getTable(): string
+	{
+		return $this->table;
+	}
+
+	/**
+	 * Create a new SELECT query.
+	 * @return SelectQuery A select query.
+	 */
+	public function newSelect(): SelectQuery
+	{
+		return new SelectQuery($this->getDatabase(), $this->getTable());
+	}
+
+	/**
+	 * Create a new INSERT query.
+	 * @return InsertQuery An INSERT query.
+	 */
+	public function newInsert(): InsertQuery
+	{
+		return new InsertQuery($this->getDatabase(), $this->getTable());
+	}
+
+	/**
+	 * Create a new UPDATE query.
+	 * @return UpdateQuery An UPDATE query.
+	 */
+	public function newUpdate(): UpdateQuery
+	{
+		return new UpdateQuery($this->getDatabase(), $this->getTable());
+	}
+
+	/**
+	 * Create a new DELETE query.
+	 * @return DeleteQuery A DELETE query.
+	 */
+	public function newDelete(): DeleteQuery
+	{
+		return new DeleteQuery($this->getDatabase(), $this->getTable());
+	}
+}
diff --git a/src/Query/Raw.php b/src/Query/Raw.php
new file mode 100644
index 0000000..ebe7d2f
--- /dev/null
+++ b/src/Query/Raw.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Nest\Database\Query;
+
+/**
+ * Raw SQL content.
+ */
+readonly class Raw
+{
+	/**
+	 * Create new raw SQL content.
+	 * @param string $sql Raw SQL content.
+	 * @param array $bindings Raw SQL bindings.
+	 */
+	public function __construct(public string $sql, public array $bindings = [])
+	{
+	}
+
+	public function __toString(): string
+	{
+		return $this->sql;
+	}
+}
diff --git a/src/Query/SelectQuery.php b/src/Query/SelectQuery.php
new file mode 100644
index 0000000..2681d54
--- /dev/null
+++ b/src/Query/SelectQuery.php
@@ -0,0 +1,135 @@
+<?php
+
+namespace Nest\Database\Query;
+
+use Nest\Database\Database;
+use Nest\Database\Query\Join\HasJoin;
+use Nest\Database\Query\Where\HasWhere;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+
+/**
+ * Builder of a SELECT query.
+ */
+class SelectQuery
+{
+	use HasJoin;
+	use HasWhere;
+
+	/**
+	 * Selected columns.
+	 * @var (Raw|string)[]
+	 */
+	protected array $selected = [];
+
+	/**
+	 * Limit of results to get.
+	 * NULL = no limit.
+	 * @var int|null
+	 */
+	protected ?int $limit = null;
+
+	/**
+	 * Create a new SELECT query.
+	 * @param Database $database The database on which to execute the query.
+	 * @param string $table Base table of the SELECT query.
+	 */
+	public function __construct(protected Database $database, protected string $table)
+	{}
+
+	/**
+	 * Get the database on which to execute the query.
+	 * @return Database
+	 */
+	public function getDatabase(): Database
+	{
+		return $this->database;
+	}
+
+	/**
+	 * Get retrieved table name.
+	 * @return string Selected table name.
+	 */
+	public function getTableName(): string
+	{
+		return $this->table;
+	}
+
+	/**
+	 * Reset selected columns.
+	 * @return $this
+	 */
+	public function resetSelect(): static
+	{
+		$this->selected = [];
+		return $this;
+	}
+
+	/**
+	 * Add selected columns.
+	 * @param string|Raw ...$selectedColumns Selected columns.
+	 * @return $this
+	 */
+	public function select(string|Raw ...$selectedColumns): static
+	{
+		// Append SELECTed columns.
+		array_push($this->selected, ...$selectedColumns);
+		return $this;
+	}
+
+	/**
+	 * Add raw selected SQL.
+	 * @param string ...$rawSelect Raw selected SQL.
+	 * @return $this
+	 */
+	public function selectRaw(string ...$rawSelect): static
+	{
+		// Append raw SQL SELECT.
+		array_push($this->selected, ...array_map(fn (string $rawSql) => new Raw($rawSql), $rawSelect));
+		return $this;
+	}
+
+	/**
+	 * Set the new limit of results.
+	 * @param int|null $limit Limit of retrieved results. NULL to remove the limit.
+	 * @return $this
+	 */
+	public function limit(?int $limit): static
+	{
+		$this->limit = $limit;
+		return $this;
+	}
+
+	/**
+	 * Build SELECT query.
+	 * @return Raw SQL and its bindings.
+	 * @throws MissingConditionValueException
+	 */
+	public function build(): Raw
+	{
+		// Build SELECT query and return its result.
+		return $this->database->getQueriesAdapter()->buildSelect($this->table,
+			// Select all columns by default.
+			empty($this->selected) ? [new Raw("*")] : $this->selected,
+			$this->joins,
+			$this->wheres,
+			$this->limit,
+		);
+	}
+
+	/**
+	 * Execute SELECT query.
+	 * @return object[] SELECT query result.
+	 * @throws MissingConditionValueException
+	 */
+	public function execute(): array
+	{
+		// Execute built query and return result.
+		return $this->database->getQueriesAdapter()->select($this->table,
+			// Select all columns by default.
+			empty($this->selected) ? [new Raw("*")] : $this->selected,
+			$this->joins,
+			$this->wheres,
+			$this->limit,
+		);
+	}
+}
diff --git a/src/Query/UpdateQuery.php b/src/Query/UpdateQuery.php
new file mode 100644
index 0000000..a1046e7
--- /dev/null
+++ b/src/Query/UpdateQuery.php
@@ -0,0 +1,80 @@
+<?php
+
+namespace Nest\Database\Query;
+
+use Nest\Database\Database;
+use Nest\Database\Query\Where\HasWhere;
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+
+/**
+ * Builder of an UPDATE query.
+ */
+class UpdateQuery
+{
+	use HasWhere;
+
+	/**
+	 * Set values.
+	 * @var array<string, Raw|string|int|float|null>
+	 */
+	protected array $set = [];
+
+	/**
+	 * Create a new UPDATE query.
+	 * @param Database $database The database on which to execute the query.
+	 * @param string $table Base table of the UPDATE query.
+	 */
+	public function __construct(protected Database $database, protected string $table)
+	{}
+
+	/**
+	 * Get the database on which to execute the query.
+	 * @return Database
+	 */
+	public function getDatabase(): Database
+	{
+		return $this->database;
+	}
+
+	/**
+	 * Reset set values.
+	 * @return $this
+	 */
+	public function resetSet(): static
+	{
+		$this->set = [];
+		return $this;
+	}
+
+	/**
+	 * Add set columns values.
+	 * @param string|array<string, Raw|string|int|float|null> $column The name of the column in column mode, or an associative array of all set columns with their corresponding value.
+	 * @param Raw|string|int|float|null $value The value to set, when setting in column mode (with a column as first parameter).
+	 * @return $this
+	 */
+	public function set(string|array $column, Raw|string|int|float|null $value = null): static
+	{
+		if (is_array($column))
+		{ // The first parameter is an array, adding set values in array mode.
+			$this->set = array_merge($this->set, $column);
+		}
+		else
+		{ // The first parameter is a string, adding set value in column mode.
+			$this->set[$column] = $value;
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Execute update query.
+	 * @param bool $returning True to return inserted objects.
+	 * @return object[]|bool Updated objects if returning is true, true otherwise.
+	 * @throws MissingConditionValueException
+	 */
+	public function execute(bool $returning = false): array|bool
+	{
+		// Execute built query and return result.
+		return $this->database->getQueriesAdapter()->update($this->table, $this->set, $this->wheres, $returning);
+	}
+}
diff --git a/src/Query/Where/ConditionBuilder.php b/src/Query/Where/ConditionBuilder.php
new file mode 100644
index 0000000..879a686
--- /dev/null
+++ b/src/Query/Where/ConditionBuilder.php
@@ -0,0 +1,215 @@
+<?php
+
+namespace Nest\Database\Query\Where;
+
+use Nest\Database\Exceptions\Query\MissingConditionValueException;
+use function Nest\Database\Utils\format_object_name;
+
+class ConditionBuilder
+{
+	protected string $column;
+	protected string $operator;
+	protected mixed $value;
+	protected string $valueColumn;
+
+	/**
+	 * And conditions to append.
+	 * @var ConditionBuilder[]
+	 */
+	protected array $ands = [];
+	/**
+	 * Or conditions to append.
+	 * @var ConditionBuilder[]
+	 */
+	protected array $ors = [];
+
+	/**
+	 * Set column of the condition.
+	 * When called a second time when there's no value, set the value column.
+	 * @param string $column Column (or value column) to use.
+	 * @return $this
+	 */
+	public function column(string $column): static
+	{
+		if (empty($this->column) || !empty($this->value))
+			$this->column = $column;
+		else
+			$this->valueColumn = $column;
+
+		return $this;
+	}
+
+	/**
+	 * Set operator of the condition.
+	 * @param string $operator Operator to use.
+	 * @return $this
+	 */
+	public function operator(string $operator): static
+	{
+		$this->operator = $operator;
+		return $this;
+	}
+
+	/**
+	 * Set value of the condition.
+	 * @param mixed $value Value to use.
+	 * @return $this
+	 */
+	public function value(mixed $value): static
+	{
+		$this->value = $value;
+		return $this;
+	}
+
+	/**
+	 * Set "=" operator.
+	 * @return $this
+	 */
+	public function equals(): static
+	{
+		return $this->operator("=");
+	}
+	/**
+	 * Set "LIKE" operator.
+	 * @return $this
+	 */
+	public function like(): static
+	{
+		return $this->operator("LIKE");
+	}
+	/**
+	 * Set "EXISTS" operator.
+	 * @return $this
+	 */
+	public function exists(): static
+	{
+		return $this->operator("EXISTS");
+	}
+
+	/**
+	 * Append and conditions.
+	 * @param callable ...$conditionBuilder And conditions builders.
+	 * @return $this
+	 */
+	public function and(callable ...$conditionBuilder): static
+	{
+		foreach ($conditionBuilder as $conditionBuilderCallable)
+		{
+			$this->ands[] = $conditionBuilderCallable(new ConditionBuilder());
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Append or conditions.
+	 * @param callable ...$conditionBuilder Or conditions builders.
+	 * @return $this
+	 */
+	public function or(callable ...$conditionBuilder): static
+	{
+		foreach ($conditionBuilder as $conditionBuilderCallable)
+		{
+			$this->ors[] = $conditionBuilderCallable(new ConditionBuilder());
+		}
+
+		return $this;
+	}
+
+
+
+	/**
+	 * Build SQL AND subcondition.
+	 * @param ConditionBuilder $condition The subcondition builder.
+	 * @return array{string, string[]} The built SQL with its bindings, if there are some. Bindings can be empty or non-existent.
+	 * @throws MissingConditionValueException
+	 */
+	private function buildAndSql(ConditionBuilder $condition): array
+	{
+		[$sql, $bindings] = $condition->toSql();
+		return ["AND $sql", $bindings];
+	}
+	/**
+	 * Build SQL OR subcondition.
+	 * @param ConditionBuilder $condition The subcondition builder.
+	 * @return array{string, string[]} The built SQL with its bindings, if there are some. Bindings can be empty or non-existent.
+	 * @throws MissingConditionValueException
+	 */
+	private function buildOrSql(ConditionBuilder $condition): array
+	{
+		[$sql, $bindings] = $condition->toSql();
+		return ["OR $sql", $bindings];
+	}
+
+	/**
+	 * Build SQL of the condition.
+	 * @return array{string, string[]} The built SQL with its bindings, if there are some. Bindings can be empty or non-existent.
+	 * @throws MissingConditionValueException
+	 */
+	public function toSql(): array
+	{
+		// Build subconditions.
+		$subconditions = [
+			...array_map(
+				fn (ConditionBuilder $condition) => $this->buildAndSql($condition),
+				$this->ands,
+			), ...array_map(
+				fn (ConditionBuilder $condition) => $this->buildOrSql($condition),
+				$this->ors,
+			)
+		];
+
+		// SQL to append after current condition.
+		$appendSql = "";
+		// Values bindings to append after current condition.
+		$appendBindings = [];
+		foreach ($subconditions as [$sql, $bindings])
+		{ // Append current subcondition to SQL.
+			$appendSql .= $sql;
+			// Append current subcondition bindings.
+			array_push($appendBindings, ...$bindings);
+		}
+
+		if (!empty($this->column))
+		{ // If a column is defined, build the condition on it.
+			if (($this->operator ?? "=") === "EXISTS" || (empty($this->operator) && empty($this->value) && empty($this->valueColumn)))
+				// "EXISTS" operator, or no operator nor value are defined.
+				return ["(EXISTS ".format_object_name($this->column)." $appendSql)", $appendBindings];
+			else
+			{
+				if (!empty($this->value))
+				{ // Condition value is a bound value.
+					if (is_array($this->value))
+					{
+						$valueSql = "(".implode(",", array_fill(0, count($this->value), "?")).")";
+						$bindings = $this->value;
+					}
+					else
+					{
+						$valueSql = "?";
+						$bindings = [$this->value];
+					}
+				}
+				elseif (!empty($this->valueColumn))
+				{ // Condition value is an SQL column.
+					$valueSql = format_object_name($this->valueColumn);
+					$bindings = [];
+				}
+				else
+					// A condition value is missing.
+					throw new MissingConditionValueException("(".format_object_name($this->column)." $this->operator [...MISSING_CONDITION_VALUE...])");
+
+				// Default operator is "=".
+				$operator = $this->operator ?? "=";
+
+				return ["(".format_object_name($this->column)." $operator $valueSql $appendSql)", [...$bindings, ...$appendBindings]];
+			}
+		}
+		else
+		{ // No column defined, just return subconditions, if there are some.
+			if (str_starts_with($appendSql, "OR")) $appendSql = trim(substr($appendSql, 2));
+			if (str_starts_with($appendSql, "AND")) $appendSql = trim(substr($appendSql, 3));
+			return ["($appendSql)", $appendBindings];
+		}
+	}
+}
diff --git a/src/Query/Where/HasWhere.php b/src/Query/Where/HasWhere.php
new file mode 100644
index 0000000..343e192
--- /dev/null
+++ b/src/Query/Where/HasWhere.php
@@ -0,0 +1,154 @@
+<?php
+
+namespace Nest\Database\Query\Where;
+
+use Nest\Database\Exceptions\Query\NoPrimaryFieldException;
+use Nest\Model\Entities;
+use Nest\Model\Entity;
+
+/**
+ * Add where capacity to a query builder.
+ */
+trait HasWhere
+{
+	/**
+	 * Conditions in where clause.
+	 * @var ConditionBuilder[]
+	 */
+	protected array $wheres = [];
+
+	/**
+	 * Reset WHERE conditions.
+	 * @return $this
+	 */
+	public function resetWheres(): static
+	{
+		$this->wheres = [];
+		return $this;
+	}
+
+	/**
+	 * Add a where condition.
+	 * @param string|callable $column The column of the condition, or a condition builder callable.
+	 * @param mixed|null $operator The operator of the condition (or the value if no value is passed).
+	 * @param mixed|null $value The value of the condition.
+	 * @return $this
+	 */
+	public function where(string|callable $column, mixed $operator = null, mixed $value = null): static
+	{
+		if (is_callable($column))
+		{ // Callable condition builder.
+			$this->wheres[] = $column(new ConditionBuilder());
+		}
+		else
+		{ // Simple condition, registering it.
+			if (!empty($operator) && empty($value))
+			{ // If there are 2 parameters, considering the second one as the value, with default operator.
+				$value = $operator;
+				$operator = null;
+			}
+
+			if (!empty($value))
+			{ // A value is defined.
+				// Default operator: "=".
+				if (empty($operator)) $operator = "=";
+
+				// Create the simple condition.
+				$this->wheres[] = (new ConditionBuilder())->column($column)->operator($operator)->value($value);
+			}
+			else
+			{ // No value is given, considering a simple existence check.
+				$this->whereExists($column);
+			}
+		}
+
+		return $this;
+	}
+
+	/**
+	 * Add a where IN condition.
+	 * @param string $column The column of the condition.
+	 * @param array $values The values of the condition.
+	 * @return $this
+	 */
+	public function whereIn(string $column, array $values): static
+	{
+		return $this->where($column, "IN", $values);
+	}
+
+	/**
+	 * Add a where condition on a column as a value.
+	 * @param string $column The column of the condition.
+	 * @param string $operator The operator of the condition (or the value column if no value is passed).
+	 * @param string|null $valueColumn The value column of the condition.
+	 * @return $this
+	 */
+	public function whereColumn(string $column, string $operator, ?string $valueColumn = null): static
+	{
+		if (!empty($operator) && empty($valueColumn))
+		{ // If there are 2 parameters, considering the second one as the value, with default operator.
+			$valueColumn = $operator;
+			$operator = "=";
+		}
+
+		// Create the simple condition.
+		$this->wheres[] = (new ConditionBuilder())->column($column)->operator($operator)->column($valueColumn);
+
+		return $this;
+	}
+
+	/**
+	 * Add a where exists condition.
+	 * @param string $column The column to check for existence.
+	 * @return $this
+	 */
+	public function whereExists(string $column): static
+	{
+		// Create an existence check.
+		$this->wheres[] = (new ConditionBuilder())->column($column)->exists();
+		return $this;
+	}
+
+	/**
+	 * Add condition to find given entities.
+	 * @param Entity|Entities $entities Entity or entities to find.
+	 * @return $this
+	 * @throws NoPrimaryFieldException
+	 */
+	public function whereKeyOf(Entity|Entities $entities): static
+	{
+		// Normalize parameter to a simple entities array.
+		if ($entities instanceof Entities)
+			$entitiesArray = $entities->get();
+		else
+			$entitiesArray = [$entities];
+
+		// Initialize entities conditions.
+		$entitiesConditions = [];
+		foreach ($entitiesArray as $entity)
+		{ // Add condition for each entity to find.
+			// Get current entity primary fields and normalize it to an array.
+			$primaryFields = $entity->getPrimaryFields();
+			if (!is_array($primaryFields)) $primaryFields = [$primaryFields];
+
+			if (empty($primaryFields))
+				// If there are no primary fields, thrown an exception to ensure not to do something on EVERY rows.
+				throw new NoPrimaryFieldException($entity);
+
+			// Create conditions for current entity.
+			$entityConditions = [];
+			foreach ($primaryFields as $primaryField)
+				// Create a condition builder for each field.
+				$entityConditions[] = fn (ConditionBuilder $condition) =>
+					$condition->column($primaryField)->equals()->value($entity->$primaryField);
+
+			// Add the full entity condition to the entities conditions array.
+			$entitiesConditions[] = fn (ConditionBuilder $condition) => $condition->and(...$entityConditions);
+		}
+
+		// Add condition to match every entities.
+		return $this->where(fn (ConditionBuilder $condition) => (
+			$condition->or(...$entitiesConditions)
+		));
+	}
+}
diff --git a/src/Transactions/Transaction.php b/src/Transactions/Transaction.php
new file mode 100644
index 0000000..48a1d23
--- /dev/null
+++ b/src/Transactions/Transaction.php
@@ -0,0 +1,139 @@
+<?php
+
+namespace Nest\Database\Transactions;
+
+use Nest\Database\Database;
+use Nest\Database\Exceptions\NotCurrentTransactionException;
+use Symfony\Component\Uid\Uuid;
+
+/**
+ * Instance of a database transaction.
+ */
+class Transaction
+{
+	/**
+	 * UUID of the transaction.
+	 * @var string
+	 */
+	private string $uuid;
+
+	/**
+	 * Determine if the transaction is active (started and not committed nor rolled back).
+	 * @var bool
+	 */
+	private bool $active = false;
+
+	/**
+	 * Subtransaction of the current transaction.
+	 * @var Transaction|null
+	 */
+	protected ?Transaction $childTransaction = null;
+
+	/**
+	 * Create a new transaction for the given database.
+	 * @param Database $database The database.
+	 * @param Transaction|null $parentTransaction The parent transaction, if there is one.
+	 */
+	public function __construct(protected Database $database, protected ?Transaction $parentTransaction = null)
+	{
+		$this->uuid = Uuid::v4()->toString();
+	}
+
+	/**
+	 * Get UUID of the transaction.
+	 * @return string
+	 */
+	public function getUuid(): string
+	{
+		return $this->uuid;
+	}
+
+	/**
+	 * Get the parent transaction.
+	 * @return Transaction|null
+	 */
+	public function getParent(): ?Transaction
+	{
+		return $this->parentTransaction;
+	}
+
+	/**
+	 * Set the current child transaction of this transaction.
+	 * @param Transaction|null $transaction The child transaction. NULL if there is no child transaction.
+	 * @return void
+	 */
+	public function setChild(?Transaction $transaction): void
+	{
+		$this->childTransaction = $transaction;
+	}
+
+	/**
+	 * Start the transaction.
+	 * @return void
+	 * @throws NotCurrentTransactionException
+	 */
+	public function start(): void
+	{
+		// Transaction activation state changed.
+		$this->active = true;
+		$this->database->onTransactionStateChanged($this);
+
+		// Start the transaction.
+		$this->database->getQueriesAdapter()->newTransaction();
+	}
+
+	/**
+	 * Commit the transaction.
+	 * @return void
+	 * @throws NotCurrentTransactionException
+	 */
+	public function commit(): void
+	{
+		if (!$this->isActive())
+			// Do not commit a non-active transaction.
+			return;
+
+		if (!empty($this->childTransaction))
+			// First commit the child transaction, if there is one.
+			$this->childTransaction->commit();
+
+		// Transaction activation state changed.
+		$this->active = false;
+		$this->database->onTransactionStateChanged($this);
+
+		// Commit the current transaction.
+		$this->database->getQueriesAdapter()->commitTransaction();
+	}
+
+	/**
+	 * Rollback the transaction.
+	 * @return void
+	 * @throws NotCurrentTransactionException
+	 */
+	public function rollback(): void
+	{
+		if (!$this->isActive())
+			// Do not rollback a non-active transaction.
+			return;
+
+		if (!empty($this->childTransaction))
+			// First rollback the child transaction, if there is one.
+			$this->childTransaction->rollback();
+
+		// Transaction activation state changed.
+		$this->active = false;
+		$this->database->onTransactionStateChanged($this);
+
+		// Rollback the current transaction.
+		$this->database->getQueriesAdapter()->rollbackTransaction();
+	}
+
+	/**
+	 * Determine if the transaction is still active (not committed nor rolled back).
+	 * @return bool
+	 */
+	public function isActive(): bool
+	{
+		return $this->active;
+	}
+}
diff --git a/src/Utils/Sql.php b/src/Utils/Sql.php
new file mode 100644
index 0000000..aa7c788
--- /dev/null
+++ b/src/Utils/Sql.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace Nest\Database\Utils;
+
+/**
+ * Format a given SQL object name.
+ * @param string $objectName The SQL object name.
+ * @return string Formatted SQL object name.
+ */
+function format_object_name(string $objectName): string
+{
+	// Rebuild the full object name from its quoted parts.
+	return implode(".",
+		// Quote each part of the object name.
+		array_map(fn (string $part) => "\"$part\"", explode(".", $objectName))
+	);
+}