add projection example for multiple aggregates

[svalaskevicius]

@Fristi what do you think? can you spot anything that could be improved easily?

[svalaskevicius]

Hi @Fristi, any feedback on this version?

currently the projection can be replayed from the start (events ordered by their creation) regardless of where in the process was it added.

there are still some items to refactor, esp direct usage of the inMemoryDb in projections

[Fristi]

Added some comments here and there.

Overall I need to take a closer look what all constructs are doing conceptually.

[svalaskevicius]

ok, looks a bit better now I hope :)

@Fristi can you spot anything that has to be fixed before merging?

[Fristi]

Overall I think it's nice to get projections out there! There are some things we could improve here :) Sometimes I find it not easy to digest some of you code. How could we improve on that? I think with a few modifications we can clarify it a lot, what do you think?

• Private/public or local functions. If a function does not need public scope, make it local (if you need it for recursive loop or something) or make it a private one if you use it multiple times. This makes modules a bit easier to digest.
• Don't use tuples in public API's, instead use case classes. They can describe what the values in the tuples are by a good name. I essence case classes are tuples, but with names :)
• Use descriptive parameter names in case classes and functions. In the example I saw you use parameters names like k, does not really reveal what the intent of parameter is
• Rather use (implicit e: Backend[T]) for implicits if you use it multiple times. Makes the code more concise (and easier to read), since you don't have to write implictly each time.
• For concepts like Backend or EventDataConsumerQuery it doesn't reveal it's intention immediately. Would be nice to introduce some docs maybe?
• Group concepts and put them in packages or separate files.

I can help you out with refactoring some parts! For now it would be good to merge this :+1:

[svalaskevicius]

completely agree! :) in fact, I thought I am already doing most of those items :D apart from short names and no docs.

happy to update the missed parts - in the end, I will have to read this as well even after I forget how it was implemented :)

will have a skim over again and see what have I missed, thanks!

[svalaskevicius]

@Fristi are these places that you meant - https://github.com/svalaskevicius/eventflow/commit/8a34878c930644b01866e42c03d894c008300d95 ? happy to improve more if you see something obvious I missed again :)

will merge - but we can always improve this in other PRs (and I hope we will :) )

and thanks for the review!