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My activities throw exceptions from time to time during the execution, so I've implemented the Faulted methods of Activity<TInstance> to handle that, discarding the changes made in the Execute method. I thought that there's some wiring underneath in Automatonymous that makes it so that the Faulted method executes when the Execute method throws an exception and then calls the Faulted methods for the activities that were executed already. It turns out that there's no such thing, as my Faulted methods are never executed.

Should I call those myself in a try/catch block instead? I could produce the BehaviorExceptionContextProxy based on BehaviorContext and the exception thrown. The only next Behavior I could pass would be the one inserted into that Activity's Execute method, but logically that means I'm compensating in the wrong direction as that next Behavior is actually to be executed after this one succeeds, so I'd compensate too much.

I also tried to use the Catch in the state machine, which does handle the exception, however, I couldn't find any way to start the execution of the compensation flow for the activity that failed when I only have the ExceptionActivityBinder present.

Is there any good way to trigger the compensation flow of the activities?

Slowacki
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  • Automatonymous state machines are used for sagas and Activities are used for the Courier. You need to use the Courier to execute your activities and make the fallbacks to work. – Alexey Zimarev Nov 22 '18 at 15:14
  • Hm, that feels a bit unintuitive providing that using Activities is allowed out-of-the-box when modelling the state machine and the Faulted method has to be implemented for each and every of them. Anyway, thanks for the information. I think I'll rewrite the compensation using the Catch methods in state machine itself. – Slowacki Nov 22 '18 at 15:23
  • I am not sure, maybe I am missing something but I never have seen activities being used in Automatonymous state machines. – Alexey Zimarev Nov 22 '18 at 15:33
  • You can add the activities to your state machine through the Activity extension method, if you want to use a factory: https://github.com/MassTransit/MassTransit/blob/develop/src/MassTransit.AutomatonymousIntegration/ContainerActivityExtensions.cs Or just through the .Execute if you want to instantiate them on the spot: https://github.com/MassTransit/Automatonymous/blob/develop/src/Automatonymous/ThenExtensions.cs – Slowacki Nov 22 '18 at 15:40

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An activity within a state machine (using Automatonymous) is much different than an activity within Courier. Unfortunately, they both have the same name, which can create confusion.

When an activity throws an exception, the Faulted method of the next activity in the behavior is called. If that method is a regular activity method (such as .Then, .Publish, etc.) it is skipped, since the Faulted method of those activities just calls the next activity in the behavior.

A Catch activity, however, can be used to catch the exception and execute a rescue behavior (which is a sequence of activities).

Either way, the Faulted method of the activity which throws an exception within the Execute method is not called. So yes, you should use a try/catch, but allow the exception to flow back out of the Execute method so that the behavior handles it properly.

Chris Patterson
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  • Yeah, that's what I expected, got a bit confused after talking to Alexey. Thanks for the answer. That explains why my activities' .Faulted were not executed. In the end in states where activities are executed I've added the Catch and publish an event with the exception details to be handled by another activity created just for exception mitigation. – Slowacki Nov 29 '18 at 17:30