CODEWITHSUNDEEP
javaandroidfirebasefirebase-realtime-database
stack man
stack man

Reputation: 2413

Retrieve Java object by ID from Firebase

I am writing an Android app and I am trying to retrieve an object of the class User.java by ID from its Firebase pertinent table. I would like to know how to get it from Java side, as long as I tried the examples stated in Firebase Official docs but none of them is working for me.

Taking this SO question as example, I want a method with the following interface:

public User readUser(String userId);

In other words, I want to execute:

readUser(-lnnROTBVv6FznK81k3n)

and retrieve the associated User object

Thanks

--------------------------------------------------------------EDIT--------------------------------------------------------------:

I managed to get the value with this code:

public void retrieveUser(final String email){
        firebaseUsersRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot messageSnapshot: dataSnapshot.getChildren()) {
                    if(messageSnapshot.getKey().equals(Email.encodeID(email))){

                        retrievedUser = messageSnapshot.getValue(User.class);
                        break;
                    }
                }
            }

            @Override
            public void onCancelled(FirebaseError firebaseError) { }
        });
    }

Please not retrievedUser is a class attribute, thus a field. I am accessing that field from the code, but even I see it takes the value on the debugger, it is being null on the calling code.

Any hint? Can´t I just return it in the method itself, so it would be?:

public User retrieveUser(final String email);

Thanks

Upvotes: 3

Views: 3383

Answers (1)

Mohamed Ibrahim
Mohamed Ibrahim

Reputation: 3914

so here is the soultion, I didn't put it in a method though.

final String uid = "your Uid here"; 
        // Get a reference to users
        Firebase ref = new Firebase(Constants.FIREBASE_URL_USERS);
        // Attach an listener to read our users
        ref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot snapshot) {

                for (DataSnapshot user: snapshot.getChildren()) {
               //this is all you need to get a specific user by Uid
                    if (user.getKey().equals(uid)){
                        wantedUser = user.getValue(User.class);
                    }
               //**********************************************

                }
                Log.i(TAG, "onDataChange: " + wantedUser.getName());
            }
            @Override
            public void onCancelled(FirebaseError firebaseError) {
                System.out.println("The read failed: " + firebaseError.getMessage());
            }
        });

Upvotes: 3

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