Get only certain amount of children from Firebase Database

Question

In my Android app I am using this code to retrieve posts from firebase database:

ArrayList<Post> posts = new ArrayList<>();
dbRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot dsp : dataSnapshot){
                   String author = dsp.child("author").getValue().toString();
                   String text = dsp.child("author").getValue().toString();
                    posts.add(new Post(author,text));
            }
                @Override
                public void onCancelled(DatabaseError databaseError) {

                }
            });

But this returns all the posts and if there would be many of them I think it wouldn't be good idea to keep them all in memory. Is there a way to get only certain number of node's children? For example at the beginning I would like to get 10 first ones, then 10 more and so on

score 1 · Answer 1 · edited Apr 05 '20 at 19:25

1

You need to use your DataSnapShot to retrieve more specific information.

There is a Firebase guide for Android that explain how to utilize: Firebase Android Guide

If you would prefer to see on Stack OverFlow a small example this answer here seems to be doing somewhat of what you would like to achieve: Firebase Get Children

edited Apr 05 '20 at 19:25

halfer

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answered Jan 15 '17 at 23:11

L1ghtk3ira

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score 1 · Accepted Answer · answered Jan 16 '17 at 00:33

You're looking for limitToFirst() (or limitToLast()).

ArrayList<Post> posts = new ArrayList<>();
Query query = dbRef.orderByKey().limitToFirst(10);
query.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot dsp : dataSnapshot){
               String author = dsp.child("author").getValue().toString();
               String text = dsp.child("author").getValue().toString();
                posts.add(new Post(author,text));
        }
            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

See the Firebase documentation on queries for an explanation of all its capabilities.

Get only certain amount of children from Firebase Database

2 Answers2