Firestore Querying Multiple Documents From Collection

In Firestore I have a users collection and within each user document is stored a collection named favorites which contains the IDs of documents marked as favorites(stores) For exam

Solution 1:

What you're asking for is called a "join", and those types of queries are not supported by Firestore. Firestore can only use documents from a single collection at a time in a single query. (The exception is collection group queries which can use documents from multiple collections that all have the same name).

What you will have to do is query for all the documents in "favorites", and use the results of that query to individually get() each related document from "stores".

Solution 2:

A possible answer for my above question is to get all the documents IDs from Favorites collection and put them into a list and then use whereIn function to join the stores collection IDs with the favorites list IDs

The major issue, is a complete loss of real-time updating functionality when using Firebase RecyclerView

favoriteList = newArrayList<>();
        favCollection.get() //get user favorites
                .addOnCompleteListener(newOnCompleteListener<QuerySnapshot>() {
                    @OverridepublicvoidonComplete(@NonNull Task<QuerySnapshot> task) {
                        if (task.isSuccessful()) {
                            for (QueryDocumentSnapshotdocument : task.getResult()) {
                                favoriteList.add(0, document.getId());
                                Log.d("Favorites", document.getId() + " => " + document.getData());
                            }
                            query = storesCollection.whereIn(FieldPath.documentId(), favoriteList).orderBy("storeName");//FieldPath.documentId gives documents IDs in stores collection which will be filtered with the provided listattachRecyclerViewAdapter();//Initiate adapter after favorites list completion
                        } else {
                            Log.d("Favorites", "Error getting documents: ", task.getException());
                        }
                    }
                });