Listen to document changes in an arbitary collection

Question

I have 3 collections, namely x.cards, y.cards and z.cards. I'd like to sent out a notification to corresponding users whenever a new card is created in any of the 3 collections. What's the best practice to listen to all 3 collections instead of listening to each collection seperately? I wanted to invoke Cloud Functions from the app.

If I understand correctly you want to have 3 Collections in Google Firestore and 1 Cloud Function that will be triggered when a document is created in any of them? — Andrei Cusnir, Mar 28 '19 at 11:25

score 1 · Accepted Answer · answered Mar 28 '19 at 13:53

There is currently no way to listen across multiple collections in Firestore.

Allowing queries across collections is being considered, but as usual there are no timelines of when (or even if) that will be available.

Also see:

Firestore query subcollections

Listen to document changes in an arbitary collection

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