Transactions

Transactions

Starting A Transaction

// GenTx generates group of entities in a transaction.
func GenTx(ctx context.Context, client *ent.Client) error {
    tx, err := client.Tx(ctx)
    if err != nil {
        return fmt.Errorf("starting a transaction: %w", err)
    }
    hub, err := tx.Group.
        Create().
        SetName("Github").
        Save(ctx)
    if err != nil {
        return rollback(tx, fmt.Errorf("failed creating the group: %w", err))
    }
    // Create the admin of the group.
    dan, err := tx.User.
        Create().
        SetAge(29).
        SetName("Dan").
        AddManage(hub).
        Save(ctx)
    if err != nil {
        return rollback(tx, err)
    }
    // Create user "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)

    // Commit the transaction.
    return tx.Commit()
}

// rollback calls to tx.Rollback and wraps the given error
// with the rollback error if occurred.
func rollback(tx *ent.Tx, err error) error {
    if rerr := tx.Rollback(); rerr != nil {
        err = fmt.Errorf("%w: %v", err, rerr)
    }
    return err
}

You must call Unwrap() if you are querying edges off of a created entity after a successful transaction (example: a8m.QueryGroups()). Unwrap restores the state of the underlying client embedded within the entity to a non-transactable version.

The full example exists in GitHub.

Transactional Client

Sometimes, you have an existing code that already works with *ent.Client, and you want to change it (or wrap it) to interact with transactions. For these use cases, you have a transactional client. An *ent.Client that you can get from an existing transaction.

// WrapGen wraps the existing "Gen" function in a transaction.
func WrapGen(ctx context.Context, client *ent.Client) error {
    tx, err := client.Tx(ctx)
    if err != nil {
        return err
    }
    txClient := tx.Client()
    // Use the "Gen" below, but give it the transactional client; no code changes to "Gen".
    if err := Gen(ctx, txClient); err != nil {
        return rollback(tx, err)
    }
    return tx.Commit()
}

// Gen generates a group of entities.
func Gen(ctx context.Context, client *ent.Client) error {
    // ...
    return nil
}

The full example exists in GitHub.

Best Practices

Reusable function that runs callbacks in a transaction:

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 = fmt.Errorf("%w: rolling back transaction: %v", err, rerr)
        }
        return err
    }
    if err := tx.Commit(); err != nil {
        return fmt.Errorf("committing transaction: %w", err)
    }
    return nil
}

Its usage:

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)
    }
}

Hooks

Same as schema hooks and runtime hooks, hooks can be registered on active transactions, and will be executed on Tx.Commit or Tx.Rollback:

func Do(ctx context.Context, client *ent.Client) error {
    tx, err := client.Tx(ctx)
    if err != nil {
        return err
    }
    // Add a hook on Tx.Commit.
    tx.OnCommit(func(next ent.Committer) ent.Committer {
        return ent.CommitFunc(func(ctx context.Context, tx *ent.Tx) error {
            // Code before the actual commit.
            err := next.Commit(ctx, tx)
            // Code after the transaction was committed.
            return err
        })
    })
    // Add a hook on Tx.Rollback.
    tx.OnRollback(func(next ent.Rollbacker) ent.Rollbacker {
        return ent.RollbackFunc(func(ctx context.Context, tx *ent.Tx) error {
            // Code before the actual rollback.
            err := next.Rollback(ctx, tx)
            // Code after the transaction was rolled back.
            return err
        })
    })
    //
    // <Code goes here>
    //
    return err
}

Isolation Levels

Some drivers support tweaking a transaction’s isolation level. For example, with the sql driver, you can do so with the BeginTx method.

tx, err := client.BeginTx(ctx, &sql.TxOptions{Isolation: sql.LevelRepeatableRead})