Getting Sagas to work

[michelkaeser]

Hi Johannes

First, let me thank you for the work you put into this project. Getting started (with Quarkus + Axon) was quite easy with the help of it!

Currently I am trying to get Sagas to work but fail to do so on various edges.

• The CdiResourceInjector uses the Quarkus BeanManager which does not implement the required methods (createAnnotatedType, getInjectionTargetFactory, etc.)
• Calling SagaLifecycle#associateWith() throws an IllegalStateException in Scope#getCurrentScope since none is active

Did you by any chance look into getting Sagas to work before?

[JohT]

Hi Michel,

you're welcome. I'm glad that it was helpful for you. I thought of also trying out Sagas here but got carried away by many other things I was curious about 😉. So no, I didn't even try to get Sagas to work.

Draft would take some time

I tried if I can come up with at least a draft for Sagas. But even this seems to take more time. One of the reasons for that is that I took an extreme approach back then to put Axonframework behind a boundary. I'd need to introduce a boundary for typical saga annotations and most probably the DeadlineManager.

Nevertheless, if you have some code (e.g. in a fork) then I could try to help you with the problems you encountered.

CdiResourceInjector

Regarding the two points you mentioned I'm not sure if I got them right. I'll try to answer them anyway 😀.

My custom implementation of the CdiResourceInjector does not depend on Quarkus. It depends on the Jakarta EE Standard "jakarta-enterprise-cdi-api".

What you probably mean is that my CdiResourceInjector implementation needs "full" CDI (Quarkus nearly "full" is ok) and isn't compatible to CDI-lite BeanContainer, the "smaller" version of the BeanManager. When refactoring the BeanManager to a BeanContainer the two methods createAnnotatedType and createAnnotatedType will be missing.

SagaLifecycle

With my already mentioned extreme approach of putting Axonframework behind a boundary I had a similar issue as far as I remember with the AggregateLifecycle. Static method calls are harder to replace (also for testing) and so I also put those calls behind the boundary. Have a look at AggregateEventEmitterAdapter.java. This introduces a lot of additional complexity that I won't do in a real world project. On the other hand it might be that the static calls need to be wrapped or configured somehow because AxonFramework provides some kind of context for them.

I hope I could help you somehow. Otherwise just send me an example and maybe I have an idea. I'm currently not able (time-wise) to add Sagas here. But if you got something to work I'm of course curious about that.

[michelkaeser]

Finally getting back to this after not touching it since then.

What I originally wanted to tell is that https://github.com/JohT/showcase-quarkus-eventsourcing/blob/master/showcase-quarkus-eventsourcing/src/main/java/io/github/joht/showcase/quarkuseventsourcing/messaging/infrastructure/axon/inject/cdi/CdiResourceInjector.java#L44 will throw exceptions when using sagas since Quarkus' arc container/bean manager does not implement these methods, see https://github.com/quarkusio/quarkus/blob/3be8518454c54b745e1e5fb44db65044d858082b/independent-projects/arc/runtime/src/main/java/io/quarkus/arc/impl/BeanManagerImpl.java#L241

Turns out this is not that big of a deal however since the parameter resolver can be used to inject dependencies on each saga handler rather than having them as injected fields.

It is important to note that https://github.com/JohT/showcase-quarkus-eventsourcing/blob/master/showcase-quarkus-eventsourcing/src/main/java/io/github/joht/showcase/quarkuseventsourcing/messaging/infrastructure/axon/inject/cdi/AxonComponentDiscovery.java#L67 should filter out @SagaEventHandler as these will be called twice otherwise (once via regular @EventHandler and once via @SagaEventHandler (as it is also a regular event handler)).

Given that, sagas can be used if working around these limitations is feasible.