[upcaster] Provide the other upcaster examples

[lfgcampos]

Our current upcaster sample only provides a SingleEventUpcaster example. We should expand it to provide the other types as well.

Starting from the EventMultiUpcaster would be a good choice.

[VladimirTitov4]

Hello, any updates on that issue? Still waiting for some examples on EventMultiUpcaster

[smcvb]

You can find an EventMultiUpcaster sample there right now, @VladimirTitov4.
Let us know what you think!

[VladimirTitov4]

You can find an EventMultiUpcaster sample there right now, @VladimirTitov4. Let us know what you think!

Thank you for the answer @smcvb ! Actually now I doubt whether I understood EventMultiUpcaster correctly.
In javadoc it says "... upcasting one intermediate event representation to several other representations ... "

but my case was "... upcasting several intermediate event representation to several other representations ... "

e.g. I have 10 Events with one specific field, that needs to be changed to other field, and keep original event name the same.
So, I would like to upcast

1. MenuCreatedEvent {
    private String sort;
}

2. MenuUpdatedEvent {
    private String sort;
}
...
10. MenuSomethingEvent {
    private String sort;
}

so I wanted to upcast all 10 events with "sort" to "position" field in one upcaster. Is that possible ?
The reason, because I wanted to use one multi upcaster for all 10 events, because all the changes are the same

[smcvb]

I think I understand @VladimirTitov4. You have ten event types which all should be pushed through an upcaster, correct?

Well, what you can do is make the canUpcast method react to all ten event types.
In doing so, the doUpcast method of your EventUpcaster will be invoked for all ten types.
I have a different opinion on whether this is smart, however.

Sure, it minimizes the number of upcasters you have to write.
But, it will make it tough to reason about your upcaster chain.
Also, how would you name the upcaster?
Ideally, it's tied directly to the event name it upcasts.
However, if the upcaster is in charge of ten events, you'd have an extremely long class name or a class name that no longer directly reflects what it adjusts.

I'd thus go for separate upcaster implementation for each event type.
To deduplicate your code, I would introduce an abstract upcaster implementation, though.

Next to the above, I have another doubt.
From your description, I think you don't need a one-to-many upcaster.
If you want to rename the field of event-x, that's a SingleEventUpcaster acting on that event to introduce the rename.
The EventMultiUpcaster is needed as soon as a single event should change in several events.

[dxp227]

Would love an example of ContextAwareSingleEventUpcaster; I'm specifically struggling to see how one can extract event payload data from the IntermediateEventRepresentation for the purpose of adding that data to the context.

[smcvb]

Good idea, @dxp227. As it stands, I think it might take some time before we can come back to your request.
I did make an issue for it (which you can find here), by the way.

In the meantime, I would recommend you take a look at the test cases of the ContextAwareSingleEventUpcaster.
Those are, in essence, samples on how to construct a ContextAwareSingleEventUpcaster too.
You can find the test case here, by the way.

[dxp227]

I'm specifically struggling to see how one can extract event payload data from the IntermediateEventRepresentation for the purpose of adding that data to the context.

Perhaps this was non-obvious to me only 😅 but here's my solution.

@smcvb The test case provides helpful direction as well - thank you!