private static function connect()
{
self::$instance = new PDO('mysql:host=' . self::$DB_HOST . '; dbname=' . self::$DB_DATABASE, self::$DB_USER, self::$DB_PASSWORD, array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES 'utf8'"));
self::$instance->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);