QuerySetByMembers.java

public static class QuerySetByMembers{
        public void querySet(String memberId)
        {
            Query queryByMember = FirebaseDatabase.getInstance().getReference().child("sets").orderByChild("members/"+memberId);
            queryByMember.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    //Not that we are returning a list as our query is on sets
                    //so iterate through the datasnapshot and get the values
                    for (DataSnapshot data : dataSnapshot.getChildren())
                    {
                        Set set = data.getValue(Set.class);
                    }
                    
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {

                    //handle some errors here
                }
            });
        }
    }