> For the complete documentation index, see [llms.txt](https://3ks.gitbook.io/ent-zh_cn/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://3ks.gitbook.io/ent-zh_cn/dai-ma-sheng-cheng/transactions.md).

# 事务

## 开始事务

```go
// GenTx 在一个事务中创建多个群组的实体及其用户
func GenTx(ctx context.Context, client *ent.Client) error {
    tx, err := client.Tx(ctx)
    if err != nil {
        return fmt.Errorf("starting a transaction: %v", err)
    }
    hub, err := tx.Group.
        Create().
        SetName("Github").
        Save(ctx)
    if err != nil {
        return rollback(tx, fmt.Errorf("failed creating the group: %v", err))
    }
    // 为群组添加一个用户
    dan, err := tx.User.
        Create().
        SetAge(29).
        SetName("Dan").
        AddManage(hub).
        Save(ctx)
    if err != nil {
        return rollback(tx, err)
    }
    // 创建一个用户 "Ariel".
    a8m, err := tx.User.
        Create().
        SetAge(30).
        SetName("Ariel").
        AddGroups(hub).
        AddFriends(dan).
        Save(ctx)
    if err != nil {
        return rollback(tx, err)
    }
    fmt.Println(a8m)
    // Output:
    // User(id=2, age=30, name=Ariel)

    // 提交事务
    return tx.Commit()
}

// rollback 会调用 tx.Rollback，如果此时发生错误，rollback 会将该错误也包装进去。
func rollback(tx *ent.Tx, err error) error {
    if rerr := tx.Rollback(); rerr != nil {
        err = fmt.Errorf("%v: %v", err, rerr)
    }
    return err
}
```

完整的例子请查看 [GitHub](https://github.com/facebookincubator/ent/tree/master/examples/traversal).

## 事务客户端

Transactional Client，事务客户端。 有时候，你的现有代码已经使用了 `*ent.Client`，但是你想将他修改（或包装）为使用事务客户端实现。 对于这种情况：你可以从现有的事务客户端获取一个 `*ent.Client`：

```go
// WrapGen 函数将现有的 "Gen" 函数包装成事务
func WrapGen(ctx context.Context, client *ent.Client) error {
    tx, err := client.Tx(ctx)
    if err != nil {
        return err
    }
    txClient := tx.Client()
    //下面会调用 "Gen"，但是传输一个事务客户端给它；这样就不用修改 "Gen" 函数的代码。
    if err := Gen(ctx, txClient); err != nil {
        return rollback(tx, err)
    }
    return tx.Commit()
}

// Gen 函数用于创建一个群组实体。
func Gen(ctx context.Context, client *ent.Client) error {
    // ...
    return nil
}
```

完整的例子请查看 [GitHub](https://github.com/facebookincubator/ent/tree/master/examples/traversal).

## 最佳实践

在事务中运行回调函数：

```go
func WithTx(ctx context.Context, client *ent.Client, fn func(tx *ent.Tx) error) error {
    tx, err := client.Tx(ctx)
    if err != nil {
        return err
    }
    defer func() {
        if v := recover(); v != nil {
            tx.Rollback()
            panic(v)
        }
    }()
    if err := fn(tx); err != nil {
        if rerr := tx.Rollback(); rerr != nil {
            err = errors.Wrapf(err, "rolling back transaction: %v", rerr)
        }
        return err
    }
    if err := tx.Commit(); err != nil {
        return errors.Wrapf(err, "committing transaction: %v", err)
    }
    return nil
}
```

用法：

```go
func Do(ctx context.Context, client *ent.Client) {
    // WithTx helper.
    if err := WithTx(ctx, client, func(tx *ent.Tx) error {
        return Gen(ctx, tx.Client())
    }); err != nil {
        log.Fatal(err)
    }
}
```


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