Android - 对recyclerview的多个查询（Firebase）

Question

I am working with recylerviews and Firebase. I am using FirebaseUI to populate data to my recyclerview. I was wondering if it was possible to use two queries within my fragment. The query that should be executed should be dependent of if a node in the database exists.

Database Structure:

If the address child is present in the users node, my fragment should query the users node. If not it should query the routes node. Is this possible?

Basically here I am making by query which gets me all markers:

Query keyQuery = FirebaseDatabase.getInstance().getReference(sharedPreferences.getString("school", null)).child("markers");
    recyclerView = (RecyclerView) rootView.findViewById(R.id.markerRecyclerview);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));

    FirebaseRecyclerOptions<FirebaseMarker> options = new FirebaseRecyclerOptions.Builder<FirebaseMarker>()
            .setQuery(keyQuery, FirebaseMarker.class)
            .build();

Inside my onBindViewHolder method I have an onClick on each item in the recyclerview. When the item is clicked, the user goes to a new activity. In this new activity the user can press a button which will add the address node under the users/userId node. What pressing that button means is that the user have chosen that marker. So I only want to show that marker information in the recyclerview and not every marker in the database.

 holder.mView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(getActivity(),MainActivity.class);
                    intent.putExtra("databaseKey", key);
                    startActivity(intent);
                }
            });

I was thinking that: If a address and time node was inserted in the users node, I could just query this, which would make it easier.

Answer 1

This is possible, although I think you'd first need to check whether the user has selected a marker and then decide which query to attach to the FirebaseRecyclerAdapter .

To do that, it would likely be necessary to add a list of users that have selected each marker under the marker nodes, something like:

users
  userId
    selectedMarker      // the ID of the marker selected by this user
    ...
markers
  markerId
    ...
    selectedUsers       // list of user IDs that have selected this marker

Then, if the users node contains a selectedMarker value, you could use the below query to get all markers selected by this specific user:

Query query = FirebaseDatabase.getInstance().getReference()
        .child(schoolId).child("markers")
        .orderByChild("selectedUsers/"+userId).equalTo(true);

Where schoolId is from your sharedPreferences.getString("school", null) and userId is the currently logged in user's unique ID.

To check if the user has selected a marker, could be as simple as:

FirebaseDatabase.getInstance().getReference()
        .child(schoolId).child("users").child(userId)
        .addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.child("selectedMarker").exists()) {
                    // Attach above query to FirebaseRecyclerAdapter
                } else {
                    // Attach markers reference (no query) to FirebaseRecyclerAdapter
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {}
        });

However, if you just want to display the user's single selected marker, it's likely that you don't need to use the RecyclerView at all, and could just use a separate view to display details about the user's selected marker.