code: func (session *Session) Begin() error {
  	if session.isAutoCommit {
  		tx, err := session.DB().BeginTx(session.ctx, nil)
  		if err != nil {
  			return err
  		}
  		session.isAutoCommit = false
  		session.isCommitedOrRollbacked = false
  		session.tx = tx
  		session.saveLastSQL("BEGIN TRANSACTION")
  	}
  	return nil
  }
docs: // Begin a transaction