How to read same value from nodes with different keys in Firebase real-time database?

Question

So I'm trying to display a list of comments under a post in a RecyclerView. However, I always run into the problem that I can't read the correct value because I don't know how to output the right path when the keys differ.

Can somebody help me?

Here's my structure in Firebase:

Here's my code so far:

 private void loadComments() {
        DatabaseReference commentRef = mRootReference.child("comments").child(pollid).getParent().child("comment");
        Query commentQuery = commentRef.limitToLast(mCurrentPage * TOTAL_ITEMS_TO_LOAD);
        commentQuery.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    Comment comment = ds.getValue(Comment.class);
                    commentList.add(comment);
                    mAdapter.notifyDataSetChanged();
                    mCommentList.scrollToPosition(commentList.size() - 1);
                }
            }

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

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot) {

            }

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

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }

score 2 · Accepted Answer · answered Aug 29 '18 at 09:16

Seeing your database schema and your code, I assume that the pollid variable specified in your reference holds the value of LKwV ... IRyZ. So to display all the comments within this node, please use the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("comments").child(pollid).orderByChild("time");
ValueEventListener valueEventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        List<Comment> list = new ArrayList<>();
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            Comment comment = ds.getValue(Comment.class);
            commentList.add(comment);
        }

        //Do what you need to do with your list
        //Pass the list to the adapter and set the adapter
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        Log.d(TAG, databaseError.getMessage());
    }
};
query.addListenerForSingleValueEvent(valueEventListener);

Thank you, works perfectly!...But also i found out, that I made a mistake in my model class. Apperently the variable in my model had to have the same name as the node as in my Database..can you confirm this maybe? — Ronaldo, Aug 29 '18 at 10:22

score 1 · Answer 2 · edited Sep 30 '18 at 07:49

1

Try using orderByChild() in your query.

Query commentQuery = commentRef.limitToLast(mCurrentPage * TOTAL_ITEMS_TO_LOAD).orderByChild("time");

edited Sep 30 '18 at 07:49

marc_s

732,580
175
1,330
1,459

answered Aug 29 '18 at 02:20

AJ Seraspi

113
1
14

Can you maybe explain it a little bit more? Just adding it, doesn't work for me. – Ronaldo Aug 29 '18 at 02:36
Are you trying to paginate it? – AJ Seraspi Aug 29 '18 at 02:45
I was going to do it...but i forgot to delete this Part of the Code before uploading – Ronaldo Aug 29 '18 at 02:48
Maybe this link can help you https://stackoverflow.com/questions/37711220/firebase-android-pagination – AJ Seraspi Aug 29 '18 at 02:50
Pagination ist mit my Problem...i struggling to read the blue marked values – Ronaldo Aug 29 '18 at 02:53
Thank you, you pointed out to me to check my model again, the mistake was in it. I didn't name the variable exactly as in the database. – Ronaldo Aug 29 '18 at 10:24

How to read same value from nodes with different keys in Firebase real-time database?

2 Answers2