从已知 uid 中检索 firebase 中的用户名

Question

I'm quite new to Android and Java, and I'm trying to teach myself doing lockdown. Right now I'm trying to retrieve a user's name based on a known uid and can't quite figure out the syntax.

My firebase database looks like this

├── chat 
│   ├── -M5D96yP5Ac688-ZPU0C << chatId 1
│   │   ├── info
│   │   │   ├── groupName: Breakfast Club
│   │   │   ├── id: -M5D96yP5Ac688-ZPU0C
│   │   │   └── Users:
│   │   │       ├── 8J7PX3ezjMTuOiAPO1BbOGJGP1g1: true
│   │   │       └── QvmGG2vPfTrdjZBfWP2ZotajYE3: true
│   │   └──Messages
│   │           .....
├── user
│   ├── 8J7PX3ezjMTuOiAPO1BbOGJGP1g1 << userId
│   │   ├── chat:
│   │   │   ├── -M5D96yP5Ac688-ZPU0C: true << chatId 1
│   │   │   ├── -M5DQuUsTJwO6tdVUstC: true
│   │   │   └── -M5DQuUsTJwO6tdVUstC: true
│   │   ├── email: JohnBender@bkfastclub.com
│   │   ├── name: John Bender
│   │   └──notificationKey: "28cb76b1-e2cd-4fa6-bf37-38336dafc45a"
│   ├── kLdxJGA7Yyfch1TthnnAPrnyny93

I have the groupId I'm in, and the userIds of the members stored

    private void getGroupMembers() {
        String key = mChatObject.getChatId();
        ArrayList<UserObject> mMembers = mChatObject.getUserObjectArrayList();

        DatabaseReference chatInfoDb = FirebaseDatabase.getInstance().getReference().child("chat").child(key).child("info").child("users");
        DatabaseReference mUserDB = FirebaseDatabase.getInstance().getReference().child("user");
 //       Query query = mUserDB.orderByChild("uid").equalTo(chatInfoDb.getUid());


    }

I just can't quite figure out how to search through the user path and grab the names of the users and store them. Ultimately I want to display them in a RecyclerView .

Any help would be much appreciated.

Answer 1

If you are trying to get the names of the users under the chat/chatID/info/users then look at my answer

Okay if your key is actually correct, first loop through all children under chat/chatID/info/users then grab the names by calling the User node.

like this:

//chat ID
String key = mChatObject.getChatId();

//database reference (be careful for lower case or upper case names)     
DatabaseReference chatInfoDb = FirebaseDatabase.getInstance().getReference().child("chat").child(key).child("info").child("Users");
DatabaseReference mUserDB = FirebaseDatabase.getInstance().getReference().child("user");


//a first call to the `chat` node:

ValueEventListener chatListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
     //loop through children
     for(DataSnapshot ds: dataSnapshot.getChildren()){

      //this will run n times, where n is the number of children under chat/chatID/info/Users

       String userId = ds.getKey();

      //now we grab the name for every userID under chat/chatID/info/Users

      mUserDB.child(userId).addListenerForSingleValueEvent(new ValueEventListener() {

          @Override
           public void onDataChange(DataSnapshot dataSnapshot) {

               //grab the name and add it to some list 
                String name = dataSnapshot.child("name").getValue(String.class);
               list.add(name)

            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
           // log error
           Log.w(TAG, "loadPost:onCancelled", databaseError.toException());

            }

      });

     }//loop end 


    }

    @Override
    public void onCancelled(DatabaseError databaseError) {
        //log error
        Log.w(TAG, "loadPost:onCancelled", databaseError.toException());

    }
};
chatInfoDb.addValueEventListener(chatListener);