[DRAFT] Experiment: Add "indices" to entity adapter

[markerikson]

Inspired by #799 , I'm trying to add some "indices" to createEntityAdapter. The idea is that you could define secondary sorting options beyond the standard sorting for state.ids, and the entity adapter will automatically keep those updated.

I initially was looking at redux-indexers, but decided that it wasn't quite a good fit.

I'm now playing with the idea of having the sorting get done inside of the merge() function in sorted_state_adapter.

Was having trouble getting the fields of the indices option to carry through, but @msutkowski just got that working in #946 .

Still got a lot of experimenting left to do.

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[markerikson]

Got something kinda working here. Types still aren't right yet - it's showing fields in entityState.indices that don't actually exist. But the logic seems like it's mostly there.

Things that are missing:

• Generating additional select$IndexName selectors automatically
• Seeing if we can add a filtering option as well, ie:

indices: {
  usersOver40ByAge: {
    sortComparer: (a, b) => a.age - b.age,
    filter: user => user.age >= 40
  }
}

[sabarnix]

indices: {
  usersOver40ByAge: {
    sortComparer: (a, b) => a.age - b.age,
    filter: user => user.age >= 40
  }
}

I have a concerns with this. How to handle cases where filtering is dependent on some other key in state or url param. Let's say 40 (the filtering age) is user input and sort order is stored in query params. Another problem would be to determine when the dependent param has changed.

[markerikson]

@sabarnix I think at that point you'd need to do the remaining filtering outside the adapter.

Assuming this is being used as a slice reducer, you only have access to the current slice state + action anyway, and at this point in the code, you don't even have access to the rest of the slice state. So, if we decide to support any filtering at all, I think it's going to be limited to just what you can do based on a single item itself.

[dutzi]

Hey @markerikson, we have a use case for this: entities are "Segments" of shape { startTime: number; endTime: number } that need to be stored sorted by both startTime and endTime.

Currently we use a selector for getting them sorted by endTime, and let RTK manage startTime sorting, but that means we re-sort the entire array on updates (instead of pushing the updated items into a sorted array, efficiently)

I've been reading through this PR, to see if we could help, but didn't find any actionable items.

Can you please give guidance, so we could help make this happen?

Correction: I now see that the typings need some sorting out, we'll try to help with that, if that's ok.

[markerikson]

@dutzi tbh this is entirely backburnered right now. We're focusing on finalizing RTK 1.9, and after that we'll be working on RTK 2.0 that drops back compat for IE11 and such.

The biggest issue here is that there isn't a good definition or requirements for what the desired behavior should be, and that also means that there isn't a valid implementation either. This was a bit of an experiment, but definitely not ready for actual use.

If someone wants to think this topic through further and propose some API designs and behaviors, we can talk about it, and I'm definitely open to PRs. But otherwise I don't see this happening any time soon.

[dutzi]

Got it. Thanks for the quick response!