public static function getDB()
{
    static $db = null;

    if ($db === null) {
        $host = 'localhost';
        $dbname = 'php_framework';
        $username = 'root';
        $password = '';

        try {
            $connection = new PDO("mysql:host=$host;dbname=$dbname", $username, $password);

            return $connection;
        } catch (PDOException $e) {
            echo $e->getMessage();
        }
    }
}