public function setTransactionIsolationLevel($level)
    {
        switch ($level) {
            case Transaction::SERIALIZABLE:
                $this->db->createCommand('PRAGMA read_uncommitted = False;')->execute();
                break;
            case Transaction::READ_UNCOMMITTED:
                $this->db->createCommand('PRAGMA read_uncommitted = True;')->execute();
                break;
            default:
                throw new NotSupportedException(get_class($this) . ' only supports transaction isolation levels READ UNCOMMITTED and SERIALIZABLE.');
        }
    }