public function getDb($db_type, $node_type)
    {
        if ($this->isSingle()) {
            switch ($db_type) {
            case Connection::DB_TYPE:
                switch ($node_type) {
                case 'master':
                    return Connection::component()->write_conn;
                case 'slave':
                    return Connection::component()->read_conn;
                default:
                    return Connection::component()->write_conn;
                }
                case \lb\components\db\mongodb\Connection::DB_TYPE :
                return \lb\components\db\mongodb\Connection::component()->_conn;
            default:
                return false;
            }
        }
        return false;
    }