public static function get_instance() { if (isset(self::$db_conn)) { return self::$db_conn; } else { require __DIR__ . '\\config.php'; global $hostname, $username, $password, $dbname; self::$db_conn = mysqli_connect($hostname, $username, $password); mysqli_select_db(self::$db_conn, $dbname); return self::$db_conn; } }