How to Properly Use a PDO Connection Across Multiple Classes in PHP?

How to Use PDO Connection in Other Classes?

Understanding the Puzzling Error

An error message stating "Uncaught Error: Call to undefined method Database::prepare()" may arise when attempting to use a PDO connection in a separate class. This error stems from a misunderstanding of how object-oriented programming (OOP) interconnects objects.

Resolving the Issue

1. Rethink Your Database Class:
The existing Database class serves no meaningful purpose. Instead, focus on creating a wrapper class if it extends PDO's functionality.

2. Establish a Central Database Connection:
Instantiate a standalone $db object using PDO or your enhanced database class. This single connection will serve as the cornerstone for all future database activities.

3. Pass the Connection as a Constructor Parameter:
Every class requiring database access should receive the $db connection as a constructor argument. This approach guarantees seamless access to the database throughout your entire application.

A Comprehensive Example

Consider the following improved codebase:

database.php:

$host = '127.0.0.1';
$db   = 'test';
$user = 'root';
$pass = '';
$charset = 'utf8';

$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
$opt = [
    \PDO::ATTR_ERRMODE            => \PDO::ERRMODE_EXCEPTION,
    \PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
    \PDO::ATTR_EMULATE_PREPARES   => false,
];
$pdo = new \PDO($dsn, $user, $pass, $opt);

user.php:

class User {
    /* Properties */
    private $conn;

    /* Get database access */
    public function __construct(\PDO $pdo) {
        $this->conn = $pdo;
    }

    /* List all users */
    public function getUsers() {
        return $this->conn->query("SELECT username, usermail FROM user")->fetchAll();
    }
}

app.php:

include 'database.php';
$user = new User($pdo);
$list = $user->getUsers();

foreach($list as $test) {
    echo $test["username"],"\n";
}

This refined codebase exemplifies the correct usage of PDO connections in multiple classes, ensuring error-free operation and elegant coding practices.

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