I want to activate activity manually in the workflow instance

[vivek-outamation]

Issue Description

I am working with a workflow scenario where activities are event-type activities.

Initial workflow definition:

A -> B

Workflow instance is created.

Activity A is triggered and completed.

Activity B is now active.

Later, I update the workflow definition to:

A -> B
  -> C

Here, C is a newly added event-type activity running in parallel with B.

I then run alteration (migration) to update the running instance to the latest version.
The alteration succeeds without errors.

Problem

After migration, activity C is not being activated automatically.

For my use case, I need the newly added event activity (C) to be activated as part of the alteration, even though the instance was already running before the workflow change.

Question

Is this possible with the existing functionality of alterations?

If not, what is the recommended way to achieve this behavior?

My goal is that when I add a new event activity in parallel to an already running one, alteration should also activate it in the running workflow instance.

[sfmskywalker]

Yes. Updating the definition and running an alteration does not automatically infer that a newly added parallel branch should start, but the alteration system has a ScheduleActivity alteration for this exact explicit step.

After the instance has been updated to the definition containing C, schedule C by its activity ID as part of the alteration plan. If C has no execution context yet, the handler finds its parent context from the updated workflow graph and sends a ScheduleChildActivity signal, which creates and schedules the new activity instance. If it already exists and is faulted, the same handler resets it to running before scheduling it.

This should be treated as a workflow-specific migration rule: only schedule the new branch when starting it for an existing instance is semantically correct, and test it with representative persisted instances.

Relevant source: src/modules/Elsa.Alterations/AlterationTypes/ScheduleActivity.cs and src/modules/Elsa.Alterations/AlterationHandlers/ScheduleActivityHandler.cs.