Firestore: Query multiple nested collections

Question

I have a nested collection in firestore as shown below:

db-dev
        user
             user-id-1
                       events-collection
                       ...
             user-id-2
                       events-collection
                       ...
             user-id-3
                       events-collection
                       ...

I want to query all the events from events-collection. However, I also want to keep the above schema as the admin needs to view all events-collection and specific users need to view their specific collection.

The query I write now looks something like this:

const uids = await getAllUserIds(); //Returns all user ID
const promises = uids.map(element => db.collection(`db-dev/user/${element}/events-collection/`).get())

const documents = await Promise.all(promises);

I am not very confident if this is the most optimized way to query the data or should I use something else? Can somebody please help me out here?

Answer 1

To read from all events-collection collections in one go, you can use a collection group query.

For example, without any conditions, this reads all documents from all collections named events-collection:

db.collectionGroup('events-collection').get()

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If you want to read only the events-collection collections under /user, you can use the trick that Sam showed here: CollectionGroupQuery but limit search to subcollections under a particular document