static function setConfig($config, $instance = 'default')
    {
        self::$config[$instance]['dsn'] = array_key_exists('dsn', $config) ? $config['dsn'] : "";
        self::$config[$instance]['username'] = array_key_exists('username', $config) ? $config['username'] : null;
        self::$config[$instance]['password'] = array_key_exists('password', $config) ? $config['password'] : null;
        self::$config[$instance]['options'] = array_key_exists('options', $config) ? $config['options'] : array();
    }