Accessing upstream values in cache operator

[mikkel-ol]

Using request caching, the custom operator returned by createRequestsCacheOperator() expects a string as argument for the cache key. Suppose the key needs to be a compound key with a value from upstream the observable. This could be some parent ID that identifies a sort of nested store cache for that parent. For instance:

  private parentId$ = of(1); // e.g. from some other service

  public get() {
    return this.parentId$.pipe(
      switchMap((id) =>
        this.http.get<Todo[]>(`https://api.com/parent/${id}/todos`)
      ),
      tap((todos) => this._store.update(setEntities(todos))),
      skipWhileCached("todos-PARENTID") // <-- This is where I need the parent ID
    );
  }

Would it be possible with an overload, or separate operation function, that passes along emitted values (but still expects a cache key to be returned)? Something along the lines of:

  public get() {
    return this.parentId$.pipe(
      switchMap((id) =>
        this.http.get<Todo[]>(`https://api.com/parent/${id}/todos`).pipe(
          map(todos => [id, todos] as const)
        )
      ),
      tap(([_, todos]) => this._store.update(setEntities(todos))),
      skipWhileCached(([id]) => `todos-${id}`) // <-- Can an overload like this be done?
    );
  }

[NetanelBasal]

Any reason you are not using the new request result feature?

[mikkel-ol]

That should be a solution. However it seems intuitive to me that joinRequestResult should return data only for the given key

[NetanelBasal]

The purpose of joinRequestResult is to merge the result data and the relevant store slice stream

[mikkel-ol]

Right I see now that it actually doesn't contain the data itself.

It would be useful to associate a store slice with a cache key.

PR #445 can effectively be used to replace the store with cached request data, however a selector on the store by cache key is really what I'm looking for

[NetanelBasal]

I see. We don't support it.

[mikkel-ol]

Fair enough