Going "back" to a previous activity

Community Support
1

Let’s say I want to go “back” to a previous activity. Is there a way to do that? Or is the only way to do that something like this:

firstActivity()

const [goBack] = secondActivity()

if (goBack) {
firstActivity()
}

2

You can use control-flow logic such as data-based decisions or looping constructs inside your workflow code.

Maybe something like this could be useful, in your workflow code:

    // workflow method code
    while(runActivities());
     // ....

and runActivities (in your workflow class) could be

    private boolean runActivities() {
        activities.first();
        return activities.second();
    }

Just note that a single workflow execution has a 50K event history limit and you probably dont’ want to loop here too many times as each activity invocation (scheduled, started, completed events) are recorded in history.

3

Thanks for the reply @tihomir . Could you clarify what you mean by “workflow class”? Is that just the activity code, e.g. activity.js in the hello work examples? Or do you mean a helper function in the workflow code? If it’s in the activity.js code, that means that I won’t benefit from first() and second() being separate activities.

Is there a way, instead, for Temporal to reconstruct the vm state but without the step we are trying to undo? Instead of using a loop.

Thanks!

4

Helper function in the workflow code. Sorry I wrongly assumed you are using Java SDK :slight_smile: (you can tag the sdk used when you start a post btw)

Is there a way, instead, for Temporal to reconstruct the vm state but without the step we are trying to undo? Instead of using a loop.

Can you share your use case for wanting to do that? Typically you would handle an activity failure and run compensation, for example execute another activity or a set of that compensate for it.

5

Ah thanks @tihomir , I added the typescript-sdk tag!

Can you share your use case for wanting to do that?

In our case, each activity involves downstream user interaction. Users can choose to go “back” to a previous activity if they want to (essentially rewinding to a previous step in the workflow). Is the while() construct the best way to do that? Are there any lower-level APIs we could use instead that change the underlying temporal state?

Thanks again!