如何在 Android Studio 中使用来自 Firebase 数据库的查询在不使用唯一 ID 的情况下获取子节点？

Question

I have set a RecyclerAdater in Android Studio and I need to point my database to the node Courses to fetch all the child nodes (CourseDate,CourseId,...) which are 2 way deep in the node Courses without knowing their unique ids using query in firebase. So how can i do it?

Database picture

Query query= (Query) CourseDatabaseRefer.addChildEventListener( new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            dataSnapshot.getChildren();
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {
            dataSnapshot.getChildren();
        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    } );

That is what I am trying to do so that after that I can pass the query object to my FirebaseRecyclerOptions as show below;

FirebaseRecyclerOptions<AllCourses> RecyclerOption=new FirebaseRecyclerOptions.Builder<AllCourses>()
            .setQuery( query,AllCourses.class ).build();

But it seems not to be working out...any help would be appreciated.

Answer 1

which are 2 way deep in the node Courses

To solve this, you need to loop through the Courses node twice and for that, I recommend you to use the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference coursesRef = rootRef.child("Courses");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<AllCourses> list = new ArrayList<>();
        for(DataSnapshot dSnapshot : dataSnapshot.getChildren()) {
            for(DataSnapshot ds : dSnapshot.getChildren()) {
                AllCourses allCourses = ds.getValue(AllCourses.class);
                list.add(allCourses);
            }
        }

        //Do what you need to do with the list
        Log.d("TAG", list.size());
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        Log.d("TAG", databaseError.getMessage()); //Don't ignore potential errors!
    }
};
coursesRef.addListenerForSingleValueEvent(valueEventListener);