Fetch data from nested nodes in Firebase

问题

I am building my first project in android using Firebase.

I have build a Firebase's database which is having main node as post, media as its child node, media node can contain multiple values for a particular post or can have one value inside it.

So i want to fetch media child node values with particular post node.

Could you please help me out.

Any help will deeply appreciated.

Please check the screenshots below.

回答1:

Firebase ref = new Firebase(YOUR_FIREBASE_URL);
            String postNode ="KddShng........";
            ref.child("posts/"+postNode).child("media").addChildEventListener(new ChildEventListener() {
                @Override
                public void onChildAdded(DataSnapshot dataSnapshot, String s) {
                        Log.e("!_@@_Key : >",dataSnapshot.getKey()); // you will get key of Media node
                }

                @Override
                public void onChildChanged(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onChildRemoved(DataSnapshot dataSnapshot) {

                }

                @Override
                public void onChildMoved(DataSnapshot dataSnapshot, String s) {

                }

                @Override
                public void onCancelled(FirebaseError firebaseError) {

                }
            });

回答2:

First you need to read docs to know how to retrieve data from firebase.

and your data will be like this ...

final Firebase ref = new Firebase("URL/posts");
    ref.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot userSnapshot : dataSnapshot.getChildren()) {
//u can handle your variables name in GetData class
                GetData posts = userSnapshot.getValue(GetData.class);

In another way..

                DatabaseReference  databaseReference = FirebaseDatabase.getInstance().getReference().child("posts");
                String user_id = firebaseAuth.getCurrentUser().getUid();
               databaseReference.child(user_id).child("media").getValue("user_id").getValue(etc);

You might save last line as String to reuse it anywhere.

UPDATE:

And to Fitch data You have to use Firebase adapter, example

回答3:

Try something like this

FirebaseDatabase.getInstance().getReference("posts").child(UID).child("media");

Where UID is the key of the particular post node.

PS: this returns something like a promise, for which you need to attach a listener for. (because this is real time)

回答4:

If just want to fetch the value once, you can do like this.

FirebaseDatabase.getInstance().getReference("posts").child("your_post_item_id").child("media").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

              for (DataSnapshot children : dataSnapshot.getChildren()) {
                  YourMediaModel mediaItem = children.getValue(YourMediaModel.class);
                  //add you mediaItem to list that you provided
              }
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }

来源：https://stackoverflow.com/questions/42408913/fetch-data-from-nested-nodes-in-firebase