第五节 db.Update()实现分析

Update()主要用来执行读写事务。事务的开始、提交、回滚都交由tx内部控制

  1. // Update executes a function within the context of a read-write managed transaction.
  2. // If no error is returned from the function then the transaction is committed.
  3. // If an error is returned then the entire transaction is rolled back.
  4. // Any error that is returned from the function or returned from the commit is
  5. // returned from the Update() method.
  6. //
  7. // Attempting to manually commit or rollback within the function will cause a panic.
  8. func (db *DB) Update(fn func(*Tx) error) error {
  9.     t, err := db.Begin(true)
  10.     if err != nil {
  11.         return err
  12.     }
  14.     // Make sure the transaction rolls back in the event of a panic.
  15.     defer func() {
  16.         if t.db != nil {
  17.             t.rollback()
  18.         }
  19.     }()
  21.     // Mark as a managed tx so that the inner function cannot manually commit.
  22.     t.managed = true
  24.     // If an error is returned from the function then rollback and return error.
  25.     err = fn(t)
  26.     t.managed = false
  27.     if err != nil {
  28.         _ = t.Rollback()
  29.         return err
  30.     }
  32.     return t.Commit()
  33. }