Firebase Database Select By Inner Field

I have some difficulties building a query for selecting data in firebase database. My database structure is like this: I need to get all users which have contact ghopper. Here the

Solution 1:

You'd use Firebase Database queries for that:

DatabaseReference usersRef = FirebaseDatabase.getInstance().ref("users");
Query query = usersRef.orderByChild("contacts/ghopper").equalTo(true);
// My top posts by number of stars
query.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot snapshot: dataSnapshot.getChildren()) {
            System.out.println(snapshot.getKey());
        }
    }

But this requires that you define an index for each user, which doesn't scale. That is because the structure you have now is meant to allow to easily determine the users for a chat room, and you're trying the opposite.

To efficiently allow getting the chat rooms for a user, you should structure your data so that it also keep a list of users for each chat room. This is often called a secondary/reversed/inverted index.

For more examples of this see:

• Firebase query if child of child contains a value
• my answer on modeling many-to-many relationship in AskFirebase