DB Helper

class DBHelper{

    protected static $conn = null;

    public function __construct($dbname=DB_NAME,$host=DB_HOST,$user=DB_USER,$password=DB_PASSWORD){
        $this->connect($this,$dbname,$host,$user,$password);
    }

    function connect(&$context,$dbname,$host,$user,$password){
        $connectionString = "mysql:host={$host};dbname={$dbname}";
        try {
            $context->conn = new PDO($connectionString,$user,$password);
        } catch (PDOException $pe) {
            die($pe->getMessage());
        }
    }

    public function __destruct() {
        $this->conn = null;
    }
}

class DBUserHelper extends DBHelper{

    function accountLogin($username, $password){
        $request = 'SELECT *
            FROM user
            WHERE username = :username AND
                  password = :password';
        $query = self::$conn->prepare($request);
        $query->execute(
            array(':username' => $username,
                  ':password' => $password
            ));
        return $query;
     }
}