Firestore- checking if username already exists

Question

I need help with Firestore. I have a AllUsers data collection, user id-documents with each user information. I want to check if username already exists; // "That username already exists". How do I do it?

` setupBtn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            final String user_name = setupName.getText().toString();

            Map<String, Object> commentsMap = new HashMap<>();
            commentsMap.put("user_id", user_id);
            commentsMap.put("timestamp", FieldValue.serverTimestamp());
            commentsMap.put("user_name",user_name);
            firebaseFirestore.collection("AllUsers").document(user_id).set(commentsMap).addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    if(task.isSuccessful()){
                        Intent asda=new Intent(getApplicationContext(),MainActivity.class);
                        startActivity(asda);
                        finish();
                   }

                }
            });

`

You got the username, so comparing the username with the saved username in database wouldn't be hard I suppose. Looks duplicate by the way. — ʍѳђઽ૯ท, Oct 17 '18 at 19:16
Need to see the structure of the firebase firestore. Would you add the structure too? As an image or something. — ʍѳђઽ૯ท, Oct 17 '18 at 20:24

score 4 · Accepted Answer · answered Oct 18 '18 at 13:07

Hope this will help.

setupBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                final String userName = setupName.getText().toString();

                CollectionReference usersRef = firestore.collection("Users");
                Query query = usersRef.whereEqualTo("username", userName);
                query.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
                    @Override
                    public void onComplete(@NonNull Task<QuerySnapshot> task) {
                        if(task.isSuccessful()){
                            for(DocumentSnapshot documentSnapshot : task.getResult()){
                                String user = documentSnapshot.getString("username");

                                if(user.equals(userName)){
                                    Log.d(TAG, "User Exists");
                                    Toast.makeText(MainActivity.this, "Username exists", Toast.LENGTH_SHORT).show();
                                }
                            }
                        }

                        if(task.getResult().size() == 0 ){
                            Log.d(TAG, "User not Exists");
                            //You can store new user information here

                        }
                    }
                });
            }
        });

this is an amazing answer, works perfectly. but what if i wanna also check if the email already exists ? — , Aug 10 '20 at 05:44

Firestore- checking if username already exists

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