如何进行多个查询以在Firebase中填充recyclerview？

Question

I am trying to retrieve some data from firebase database and populate it to recyclerview. The logic behind the query is to display users with opposite sex as the current user but the same hall. Example if the current user is a "boy" and is in "Legon" hall, populate recyclerview with "females" in legon hall from database.

Users Database:

This is what I am trying to do but is not working

@Override
protected void onStart() {
        super.onStart();

    final String user_id = firebaseAuth.getCurrentUser().getUid();
    final User user = new User();

    final String halls = user.getHalls();


    databaseReference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot)

        {

            if(dataSnapshot.child("Male").hasChild(user_id)){


                query = databaseReference.child("Female").orderByChild("halls").equalTo(halls);
            }
            else{

                query = databaseReference.child("Male").orderByChild("halls").equalTo(halls);
            }
        }
        @Override
        public  void onCancelled(DatabaseError databaseError){

        }
    });

        FirebaseRecyclerAdapter<User, UserViewholder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<User, UserViewholder>(
        User.class,
        R.layout.users_row,
        UserViewholder.class,
        query

        ) {
@Override
protected void populateViewHolder(UserViewholder viewHolder, User model, int position) {
        viewHolder.setUsername(model.getUsername());
        viewHolder.setLevels(model.getLevels());
        viewHolder.setDownloadUrl(getApplicationContext(), model.getDownloadUrl());
        }

        };

        users2.setAdapter(firebaseRecyclerAdapter);

        }

Answer 1

I think you are wrong in here

final User user = new User();
final String halls = user.getHalls();

because halls always return null

You should change it to

User user = firebaseAuth.getCurrentUser();
final String halls = user.getHalls();