PHP Database Connections: Global, Singleton, or Factory – Which is Best?

Singleton vs. Global for Database Connections in PHP

Global variables and singletons offer alternative approaches to managing database connections in PHP. However, each approach has its advantages and disadvantages.

Global Connections

Global connections provide a straightforward and concise way to share a single database connection across the entire application.

$conn = new PDO(...);

function getSomething()
{
    global $conn;
    ...
}

However, global connections can become problematic when the application becomes more complex and requires managing multiple database connections or implementing context-awareness.

Singleton Connections

Singleton connections provide a controlled and managed approach to creating and retrieving a single instance of a database connection.

class DB_Instance
{
    private static $db;

    public static function getDBO()
    {
        if (!self::$db) {
            self::$db = new PDO(...);
        }
        return self::$db;
    }
}

function getSomething()
{
    $conn = DB_Instance::getDBO();
    ...
}

Singletons offer the advantage of centralized control over the connection instance. However, they can introduce unnecessary complexity and limit the flexibility to implement different connection configurations or strategies.

Singleton Factory

A singleton factory provides a compromise between global and singleton connections. It allows for centralized connection creation while providing flexibility to change the connection implementation or configuration later.

class ConnectionFactory
{
    private static $factory;
    private $db;

    public static function getFactory()
    {
        if (!self::$factory) {
            self::$factory = new ConnectionFactory(...);
        }
        return self::$factory;
    }

    public function getConnection()
    {
        if (!$this->db) {
            $this->db = new PDO(...);
        }
        return $this->db;
    }
}

function getSomething()
{
    $conn = ConnectionFactory::getFactory()->getConnection();
    ...
}

The connection factory pattern allows for easy customization of the connection retrieval process and enables support for features such as connection pooling, logging, or context-aware connections.

Ultimately, the best approach for managing database connections depends on the specific requirements of the application. Global connections can be suitable for simple applications with a single persistent connection. Singleton connections can offer more control but may add complexity. Singleton factories provide a balance between flexibility and control, making them a suitable choice for larger and more complex applications.

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