如何在Firebase中获取密钥

Question

I want to retrieve the messages data under a specific key. But I don't how to get the key. Please help, I'm new to firebase.

In my case right now, I want to get the key encircled below.

I have tried this code below but this returns "chat-mates" not the key.

final DatabaseReference ref =FirebaseDatabase.getInstance().getReference().child("chat").child("single-chat").child("converstation").child("chat-mates");

    ref.orderByChild("receiverName").equalTo("Liza Soberano").addListenerForSingleValueEvent(new ValueEventListener() {

        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot child: dataSnapshot.getChildren()){
                String key = child.getKey();
                Log.e("Key", key);
            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

I have tried this code below but this returns "chat-mates" not the key.

Answer 1

You must be using DataSnapshot method to access the JSON tree. The DataSnapshot element has a method called getKey() . That returns the key of an object.

Official Doc: DataSnapShot getKey() method

Example Code:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
        ref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot snapshot) {
                for (DataSnapshot objSnapshot: snapshot.getChildren()) {
                        Object obj = objSnapshot.getKey();
                }
            }
            @Override
            public void onCancelled(DatabaseError firebaseError) {
                Log.e("Read failed", firebaseError.getMessage());
            }
        });

In your case, first get to the child node "conversation" and then apply the above method getKey() .

Answer 2

You're building your path wrong and likely end up iterating a different part of the tree, one level above child-mates . In that case it would be correct that child-mates is a child key.

The problem is in the last child() call when you create the ref:

final DatabaseReference ref =FirebaseDatabase.getInstance().getReference()
    .child("chat")
    .child("single-chat")
    .child("converstation")
    .child("chat-mates");

There is no child chat-mates under converstation , so this ref won't be correct.

You probably want to do this:

final DatabaseReference ref =FirebaseDatabase.getInstance().getReference()
    .child("chat")
    .child("single-chat")
    .child("converstation");

ref.orderByChild("chat-mates/receiverName")
    .equalTo("Liza Soberano")
    .addListenerForSingleValueEvent(new ValueEventListener() {

This will filter on the chat-mates/receiverName child of each chat.

Note that you're going against one of Firebase's recommendations with this data structure. Firebase recommends against nesting data types in the way you do here.

A more denormalized data model would be:

chat-mates
  $chatRoomId
    receiverName
    senderName
chat-messages
  $chatRoomId
    $messageId

This way you can get the mates/participants in a chat, without accessing (or even needing to have access to) the messages themselves.