Get last child for each child using Firebase Database

Question

I want to get sender_uid values on the image below:

This is my code below. I don't get any values with it, and I don't know why. Can someone explain what is wrong with the code? Thanks!

EDIT: I only want the last sender_uid for each parent - for example:

for node 391rfBEXjVUplEW8aoahMtluSmz1_6dTv7oHnWOh55XzRuf9ouZFZkGt2
I need only sender_uid from LJxvDjdetWz1-DAFVCy, NOT from LJxvA65WA7MX8aaX5nF.

mDatabase.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            List<UsersListGetter> usersList = new ArrayList<>();
            recyclerView.setAdapter(new UsersListAdapter(usersList, getApplicationContext()));

            recyclerView.setAdapter(new UsersListAdapter(null, getApplicationContext()));

            for (DataSnapshot ch : dataSnapshot.getChildren()) {
                String senderReceiver[] = ch.getKey().split("_");

                if (senderReceiver[0].equals(mAuth.getUid()) || senderReceiver[1].equals(mAuth.getUid())) {
                    Query lastQuery = mDatabase.child(ch.getKey()).orderByKey().limitToLast(1);
                    lastQuery.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            String message = dataSnapshot.child("message_body").getValue().toString();
                            Log.d("MSG", message);
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {
                            //Handle possible errors.
                        }
                    });
                }
            }
        }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {

    }
});

Possible duplicate of [i need to get Last child of my firebase databse](https://stackoverflow.com/questions/43557122/i-need-to-get-last-child-of-my-firebase-databse) — Usman Ali, Aug 16 '18 at 13:08

score 1 · Answer 1 · answered Aug 15 '18 at 17:25

You can do it this way to get the sender_uid from each node

First create a pojo class to get your desired data

public class UserPojo {

    private String sender_uid;

    public UserPojo() {

    }

    public String getSender_uid() {
        return sender_uid;
    }

    public void setSender_uid(String sender_uid) {
        this.sender_uid = sender_uid;
    }
}

and then just retrieve it for each chat ref

mDatabase.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                List<UsersListGetter> usersList = new ArrayList<>();
                recyclerView.setAdapter(new UsersListAdapter(usersList, getApplicationContext()));

                recyclerView.setAdapter(new UsersListAdapter(null, getApplicationContext()));

                for (DataSnapshot ch : dataSnapshot.getChildren()) {
                  UserPojo up = ch.getValue(UserPojo.class);
                  String senderUid = up.getSender_uid(); //here you got your sender_uid

                        Query lastQuery = mDatabase.child(ch.getKey()).orderByKey().limitToLast(1);
                        lastQuery.addListenerForSingleValueEvent(new ValueEventListener() {
                            @Override
                            public void onDataChange(DataSnapshot dataSnapshot) {
                                String message = dataSnapshot.child("message_body").getValue().toString();
                                Log.d("MSG", message);
                            }

                            @Override
                            public void onCancelled(DatabaseError databaseError) {
                                //Handle possible errors.
                            }
                        });

                }
            }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });

Thank you for response! I forgot to mention - is it possible to get only **last** *sender_uid* for each parent? — unipin, Aug 15 '18 at 18:06

score 0 · Answer 2 · answered Aug 16 '18 at 12:27

Assuming that the chat node is a direct child of your Firebase root, to solve this, please use the following query:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef
    .child("chat")
    .child(receiver_id + "_" + sender_uid)
    .orderByChild("sender_uid")
    .limitToLast(1);
query.addListenerForSingleValueEvent(/* ... */);

Get last child for each child using Firebase Database

2 Answers2