how to check the current Firebase data under uid?

Issue

I am trying to check uid from firebase Realtime database, but its only returns the current uid and when I try to check uid with previous uid then also it only returns the current uid. I had tried many ways and searched but I can't get the exact solution, please if any one could help.

here what I am using to check the uid

FirebaseAuth.getInstance().getCurrentUser().getUid();

here is my code how I am trying to check

 String userEnteredUserName = binding.textLoginUserName.getEditText().getText().toString().trim();
 String userEnteredPassword = binding.textPassword.getEditText().getText().toString().trim();
 DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");
    Query checkUser = reference.child(FirebaseAuth.getInstance().getCurrentUser().getUid()).orderByChild("userName").equalTo(userEnteredUserName);
    Log.d("uids", "uid: " + uid);
    checkUser.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot snapshot) {
            binding.textLoginUserName.setError(null);
            binding.textLoginUserName.setErrorEnabled(false);
            Log.d("users", "Username: " + snapshot.toString());

            if (snapshot.exists()) {
                String passwordFromDB = snapshot.child(userEnteredUserName).child("password").getValue(String.class);
                if (passwordFromDB.equals(userEnteredPassword)) {
      //next activity
}else{
Toast.makeText(Login.this, "Error", Toast.LENGTH_SHORT).show();
}
        }

        @Override
        public void onCancelled(@NonNull DatabaseError error) {

            Toast.makeText(Login.this, "Error", Toast.LENGTH_SHORT).show();

        }
    });

In log what I get,

2022-02-06 13:13:06.173 18093-18093/abc C/uids: uid: OFtpR6bfISP3Odd9K1oGWCQmeEf2

Here is my firebase data, "aisha12" is working which is under the current uid but when I try to check "vgbb" it returns only the current uid

Solution

If I understand correctly, you are trying to allow a user to register a username and ensuring that the username is unique. Your current data structure doesn't allow you to do that query though.

Firebase Realtime Database can only order/filter on a value that is at a fixed path under each child node of the location you query. So in your current code:

reference.child(FirebaseAuth.getInstance().getCurrentUser().getUid()).orderByChild("userName").equalTo(userEnteredUserName);

You are querying the direct child nodes of /Users/$uid looking for the username under there. Since you're specifying the UID in that path, you're only searching under that specific user.

There is no way with your current data structure to search across all /Users, since the property you are looking for is under /Users/$uid/$username/userName, so with two dynamic keys in there, and the database can only handle one dynamic key.

---

To allow the query, you will need to change the data structure and remove the $userName level from it, so that you get:

Users: {
  "3l6Rm....": {
    "userName": "vgbb",
    ...
  },
  "OftpR...": {
    "userName": "aisha12",
    ...
  }
}

Now you can search for the username with:

DatabaseReference reference = FirebaseDatabase.getInstance().getReference("Users");

Query checkUser = reference.orderByChild("userName").equalTo(userEnteredUserName);

I also recommend checking out these previous questions on allowing a user to register a unique username:

• How do you prevent duplicate user properties in Firebase?
• Firebase security rules to check unique value of a child #AskFirebase
• How to check if usernames are unique in Firebase
• unique property in Firebase
• How to give unique usernames from a list of usernames to the users in the firebase
• Check value already exists or not in Firebase?

Answered By - Frank van Puffelen