第四节 db.View()实现分析

View()主要用来执行只读事务。事务的开启、提交、回滚都交由tx控制。

  1. // View executes a function within the context of a managed read-only transaction.
  2. // Any error that is returned from the function is returned from the View() method.
  3. //
  4. // Attempting to manually rollback within the function will cause a panic.
  5. func (db *DB) View(fn func(*Tx) error) error {
  6.     t, err := db.Begin(false)
  7.     if err != nil {
  8.         return err
  9.     }
  11.     // Make sure the transaction rolls back in the event of a panic.
  12.     defer func() {
  13.         if t.db != nil {
  14.             t.rollback()
  15.         }
  16.     }()
  18.     // Mark as a managed tx so that the inner function cannot manually rollback.
  19.     t.managed = true
  21.     // If an error is returned from the function then pass it through.
  22.     err = fn(t)
  23.     t.managed = false
  24.     if err != nil {
  25.         _ = t.Rollback()
  26.         return err
  27.     }
  29.     if err := t.Rollback(); err != nil {
  30.         return err
  31.     }
  33.     return nil
  34. }