mongo manual session failed

[Mikaelemmmm]

When mongo manually opens a transaction, the second parameter of mongo.NewSessionContext needs to pass its own session inside the mongo sdk, but this session cannot be obtained within the framework. I currently obtain it through reflection. The following is my temporary solution.

When performing specific db insert, update and other operations, it will be judged whether the session injected into ctx when mongo.NewSessionContext is its own session within the SDK. If not, it will not be treated as an open transaction.

mongo sdk logic:

https://github.com/mongodb/mongo-go-driver/blob/v1/mongo/collection.go#L268

https://github.com/mongodb/mongo-go-driver/blob/v1/mongo/session.go#L383

var ErrMongoSessionEmpty = errors.New("Start Transaction Mongo Session Empty")

func StartTransaction(ctx context.Context, client *mon.Model, txnFunc func(sc mongo.SessionContext) error) error {

	session, err := client.StartSession()
	if err != nil {
		return err
	}
	defer session.EndSession(ctx)

	err = session.StartTransaction()
	if err != nil {
		return err
	}

	// -------- need mongo sdk client session --------
	mongoSession := getMongoSession(session)
	if mongoSession == nil {
		return ErrMongoSessionEmpty
	}
	sessCtx := mongo.NewSessionContext(ctx, mongoSession)
	//  -------- need mongo sdk client session  -------- 
	
	
	defer func() {
		if err != nil {
			if abortErr := session.AbortTransaction(sessCtx); abortErr != nil {
				logx.WithContext(ctx).Errorf("session rollback failed , err:%v，abortErr：%v", err, abortErr)
			}
		}
	}()

	err = txnFunc(sessCtx)
	if err != nil {
		return err
	}

	err = session.CommitTransaction(sessCtx)
	if err != nil {
		return err
	}

	return nil
}

//  get mongo sdk session from reflection
func getMongoSession(sess mongo.Session) mongo.Session {
	sessValue := reflect.ValueOf(sess)
	if sessValue.Kind() == reflect.Ptr {
		sessValue = sessValue.Elem()
	}
	field := sessValue.FieldByName("Session")
	if field.IsValid() && field.CanInterface() {
		if innerSess, ok := field.Interface().(mongo.Session); ok {
			return innerSess
		}
	}
	return nil
}