[signalStore] Best practice for reacting to a signal within an rxMethod pipe chain

[jits]

Thinking of the classic switchMap (or other flattening operator) approach to switch to another observable and keep a live "channel" open, e.g.:

pipe(
  switchMap((id) => {
    return this.otherService.get$(id).pipe(...);
  }),
 ...
}

What would the equivalent approach and best practice be to switch to an observable from a signal (i.e. react to changes to that signal, e.g. in an rxMethod within a signalStore method)?

An initial idea:

pipe(
  switchMap((id) => {
    return toObservable(this.otherService.getSignal(id));
  }),
 ...
}

… i.e. using the toObservable helper from @angular/core/rxjs-interop.

EDIT: the above currently doesn't work (in a SignalStore) as it throws an injection error (it needs to be run within an injection context).

But is there a better way?

[jits]

As discussed / identified in #4122 (hat tip to @e-oz), here is a solution that seems to be working well for me:

BEFORE:

pipe(
  switchMap((id) => {
    return this.otherService.get$(id).pipe(...);
  }),
 ...
}

AFTER:

pipe(
  combineLatestWith(toObservable(this.otherService.getSignal(id))),
  switchMap(([id, signalValue]) => {
    return …;
  }),
 ...
}

Note these are not fully equivalent and may exhibit subtle differences based on how you use them (for more on this it's worth digging into how the inner observable within a switchMap [or other flattening operator works] works vs how combineLatestWith combines multiple source observables at a higher level).