I have some RxFire code that listens to a Firestore collection query (representing channels) and, for each of the results, listens to a Realtime Database ref for documents (representing messages in that channel).
The problem I'm running into is that the Realtime Database documents are re-downloaded every time the Firestore query changes, even if they're for a path/reference that hasn't changed.
Here's some pseudo-code:
collection(channelsQuery).pipe(
// Emits full array of channels whenever the query changes
switchMap(channels => {
return combineLatest(
channels.map(channel =>
// Emits the full set of messages for a given channel
list(getMessagesRef(channel)),
),
);
})
)
Imagine the following scenario:
- Query intially emits 3 Firestore channel documents
- Observables are created for corresponding Realtime Database refs for those 3 channels, which emit their message documents
- A new Firestore document is added that matches the original query, which now emits 4 channel documents
- The previous observables for Realtime Database are destroyed, and new ones are created for the now 4 channels, re-downloading and emitting all the data it already had for the previous 3.
Obviously this is not ideal as it causes a lot of redundant reads on the Realtime Database. What's the best practice in this case? Keep in mind that when a channel is removed, I would like to destroy the corresponding observable, which switchMap already does.
