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

// Update executes a function within the context of a read-write managed transaction.
// If no error is returned from the function then the transaction is committed.
// If an error is returned then the entire transaction is rolled back.
// Any error that is returned from the function or returned from the commit is
// returned from the Update() method.
//
// Attempting to manually commit or rollback within the function will cause a panic.
func (db *DB) Update(fn func(*Tx) error) error {
    t, err := db.Begin(true)
    if err != nil {
        return err
    }

    // Make sure the transaction rolls back in the event of a panic.
    defer func() {
        if t.db != nil {
            t.rollback()
        }
    }()

    // Mark as a managed tx so that the inner function cannot manually commit.
    t.managed = true

    // If an error is returned from the function then rollback and return error.
    err = fn(t)
    t.managed = false
    if err != nil {
        _ = t.Rollback()
        return err
    }

    return t.Commit()
}