Transactions

precondition：

• Version of mongoDB server >= v4.0
• Topology of mongoDB server should be replica set

Usage

• You can use transactions:

callback := func(sessCtx context.Context) (interface{}, error) {
    // Important: make sure the sessCtx used in every operation in the whole transaction
    if _, err := cli.InsertOne(sessCtx, bson.D{{"abc", int32(1)}}); err != nil {
        return nil, err
    }
    if _, err := cli.InsertOne(sessCtx, bson.D{{"xyz", int32(999)}}); err != nil {
        return nil, err
    }
    return nil, nil
}
result, err = cli.DoTransaction(ctx, callback)

• At the same time, you can create session and use session to start transaction: （Don't forget to call EndSession if session is not used anymore）

s, err := cli.Session()
defer s.EndSession(ctx)

callback := func(sessCtx context.Context) (interface{}, error) {
    // Important: make sure the sessCtx used in every operation in the whole transaction
    if _, err := cli.InsertOne(sessCtx, bson.D{{"abc", int32(1)}}); err != nil {
        return nil, err
    }
    if _, err := cli.InsertOne(sessCtx, bson.D{{"xyz", int32(999)}}); err != nil {
        return nil, err
    }
    return nil, nil
}

_, err = s.StartTransaction(ctx, callback)

notes

• Make sure all operations in transaction use the sessCtx as context parameter

• Don't forget to call EndSession after action is done, if you create session yourself.

• Timeout: If operations in transaction takes more than(include equal) 120s, the operations will not take effect

• Retry: If operations in transaction return qmgo.ErrTransactionRetry, the whole transaction will retry, so this transaction must be idempotent.

  check TestSession_RetryTransAction in retry example

• If the ctx parameter already has a Session attached to it, it will be replaced by this session.

• In MongoDB 4.2 and earlier, you cannot create collections in transctions. Write operations that result in document inserts (e.g. insert or update operations with upsert: true) must be on existing collections if run inside transactions.

• Starting in MongoDB 4.4, you can create collections in transactions implicitly or explicitly. You must use MongoDB drivers updated for 4.4, however. See Create Collections and Indexes In a Transaction for details.

• More examples

• Official manual about transactions