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What I learned from 3 years of CQRS and FP

I am currently setting up part of a BC for a customer, and it took me some refactoring after having not done any serious .Net for a few years, but I got there in the end; here is how I structured my current software project in .Net.

I think it is a reasonable base, easy to extend; some remarks:

  • I use test-after, having readable scenarios that run directly on controllers, using the fake infrastructure; I verify both models, view names and redirects.
  • IOther*-interfaces implement services, but are expressed in the ubiquitous language, so f.e.:
    • Wrong: EmailService.SendEmail
    • Right: Notifier.SendInvitation (you don’t wan’t things like mail composition in your domain code).
  • IInfo-interface implements events and domain queries, f.e.:
    • Wrong: UpdateAuthenticationId or GetItemLine(id).code
    • Correct: UserAuthenticationSucceeded of GetItemCode(id)
  • I don’t expose messages to the domain model. After all, messages are an implementation detail part of the transport layer. I learned this from Erlang where messages are first class members, but people still wrap the sending in a public interface.
  • For now infrastructure tests are manually ( a staging environment needs to be provisioned later on; the change is low in these).
  • The only thing I query from the domain model in the controllers is decision state (i.e. should it proceed with the registration or not, typically using enums).
  • My IInfo events and queries used by the domain model modify the SQL server data directly.
  • My IViews are only used to populate controller views.
  • If I want to debug/run locally, I can replace all the non-relevant Infrastructure components with their Infrastructure.Fakes counter-parts in the container configuration.
  • My Infrastructure.Fakes contain extra methods to verify f.e. whether an invocation has happened, and I use a distinct naming convention to make this obvious, f.e. was_invitation_sent.

Conclusion

So, that’s it: the way I currently implemented several .Net sites for a bounded context. Tomorrow I am having a review with one of my peers, so I’m expecting it to be an interesting discussion - looking forward to it - !

I hope this makes any sense at all, and if you have further questions: shoot!

Cheers,

T.

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