如何从Firebase实时数据库中具有不同键的节点读取相同的值？

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) {

            }
        });
    }

Answer 1

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);

Answer 2

尝试在查询中使用orderByChild（）。

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