How to order firebase data from the latest

Question

Firebase by default orders data from the earliest and I need it to be ordered from the latest.

I am using timestamp to do so and doesn't seem to be working.

 private void filldata() {
        mDatabase.child("Data").orderByChild("timestamp").addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(DataSnapshot  snapshot, String s) {
                System.out.println("snapshot:" + snapshot.toString());
            }
}

score 2 · Answer 1 · answered Jun 03 '18 at 17:04

You no need to use orderByChild() here in your case because firebase itself generate unique key which is based on a timestamp, so you can simply use orderByKey() in your query and you will get your data in latest order.

The unique key is based on a timestamp, so list items will automatically be ordered chronologically. Because Firebase generates a unique key for each blog post, no write conflicts will occur if multiple users add a post at the same time. You can find more here

parag pawar · Answer 2 · 2018-06-03T12:36:36.447

1

I'll suggest to use

mDatabase.child("Data").orderByKey().limitToLast(no_of_items_you_want)

This will give you list of latest data

Also to get value from snapshot use

snapshot.getValue(String.class);

edited Jun 03 '18 at 12:36

answered Jun 03 '18 at 12:34

parag pawar

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it'll work if you have used push() method while uploading...show that code also – parag pawar Jun 04 '18 at 05:27

score 0 · Answer 3 · answered Jun 03 '18 at 10:16

0

Since orderByChild() only sort data in ascending order, you should store an extra data item in your child node whith the value timestamp*(-1) and then sort (order) on this data item.

answered Jun 03 '18 at 10:16

Renaud Tarnec

79,263
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You can reverse from recyclerView that worked for me. – Vincent Macharia Jun 18 '18 at 11:03

score 0 · Answer 4 · answered Jun 03 '18 at 20:45

Your code is correct. The commonly suggested way to order will be by using a negative timestamp.

However I have noticed previously that firebase does order your results by timestamp, as you currently wish for it to do. When the device receives the results it reorders the results by arrival (suspicion).

To test this, try limit your results by using the .limitToLast(n) function, you will realize that while firebase will return the last 10 (in order of timestamp) results to you, these results will not be ordered by timestamp.

Therefore, the best solution will be to store the firebase results in a list and reorder the list using a sorting tool like a comparator

How to order firebase data from the latest

4 Answers4