如何从firebase检索相同的数据？

Question

I have some problems in retrieving data from firebase. I want to retrieve users' emails to listview in which username are same. I want to get all users' emails whose names are same as me. I have no idea on how to do that as I am new to android.

Here is my database structure. Greens are uid.

Can You Tell Me How To Easily Retrieve Them To A Listview?

Answer 1

For this, you can use orderByChild() along with equalTo() to compare the username to what you intend and then get their email.

What I am saying, looks something like this in code:

DatabaseReference ref = FirebaseDatabase.getInstance().getReference().child("details");

  ref.orderByChild("username").equalTo(userNameYouWant).addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                            for (DataSnapshot ds : dataSnapshot.getChildren()){
                                 email.add(ds.child("email").getValue(String.class)); // email here is the ArrayList where you need to add the email
                            }

                        }

                        @Override
                        public void onCancelled(@NonNull DatabaseError databaseError) { // ToDo: don't ignore this, do something for errors

                        }
                  )};                     

This code above, compares all the usernames to the userNameYouWant and if it matches, it adds the value in their email node to the email ArrayList.