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本文主要研究一下gorm的Transaction

Transaction

gorm.io/gorm@v1.20.10/finisher_api.go

// Transaction start a transaction as a block, return error will rollback, otherwise to commit.
func (db *DB) Transaction(fc func(tx *DB) error, opts ...*sql.TxOptions) (err error) {
    panicked := true

    if committer, ok := db.Statement.ConnPool.(TxCommitter); ok && committer != nil {
        // nested transaction
        if !db.DisableNestedTransaction {
            err = db.SavePoint(fmt.Sprintf("sp%p", fc)).Error
            defer func() {
                // Make sure to rollback when panic, Block error or Commit error
                if panicked || err != nil {
                    db.RollbackTo(fmt.Sprintf("sp%p", fc))
                }
            }()
        }

        if err == nil {
            err = fc(db.Session(&Session{}))
        }
    } else {
        tx := db.Begin(opts...)

        defer func() {
            // Make sure to rollback when panic, Block error or Commit error
            if panicked || err != nil {
                tx.Rollback()
            }
        }()

        if err = tx.Error; err == nil {
            err = fc(tx)
        }

        if err == nil {
            err = tx.Commit().Error
        }
    }

    panicked = false
    return
}

DB的Transaction方法针对非TxCommitter类型的db.Statement.ConnPool执行db.Begin，之后注册defer针对panicked或者err的执行tx.Rollback()，执行fc之后，判断err为nil的情况下执行tx.Commit()，并将Error赋值为err

实例

func TestInsertInTx(t *testing.T) {
    err := db.Transaction(func(tx *gorm.DB) error {
        classes := []model.Class{
            {
                Name: "abc2",
            },
            {
                Name: "abc2",
            },
        }
        err := db.Create(&classes).Error
        if err != nil {
            return err
        }

        uc := []model.UserClass{
            {
                UserId: 1,
                ClassId: classes[0].ID,
            },
            {
                UserId: 1,
                ClassId: classes[1].ID,
            },
        }
        err2 := db.Create(&uc).Error
        if err2 != nil {
            return err2
        }

        return nil
    })

    if err != nil {
        t.Error(err)
    }
}

小结

gorm的DB提供了Transaction方法，相当于一个事务模板，自动commit或者rollback，它提供了func(tx *gorm.DB) error参数用于自定义事务内的数据库操作。

doc

• gorm