Java – Firebase query logic does not work in Android

I want to make a query to check if a certain name (president or secretary) exists in the database.
The database structure is as follows.

I have this code but it doesn’t work. Am I doing something wrong?

mDatabase = FirebaseDatabase.getInstance().getReference();
        Query presidentquery = mDatabase.child("validate").child(uid).equalTo("President");
        presidentquery.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                if (dataSnapshot.exists()) {
                    for (DataSnapshot dataSnapshot1 : dataSnapshot.getChildren()) {
                        Candidate p = dataSnapshot1.getValue(Candidate.class);
                        president.setEnabled(false);
                        president.setText("Voted Already");
                    }
                }
                else{

president.setOnClickListener(new View.OnClickListener() {
                        @Override
                        public void onClick(View v) {

startActivity(new Intent(Home.this, AllCandidates.class));
                            finish();
                        }
                    });
                }
            }
            @Override
            public void onCancelled(DatabaseError databaseError) {
            }
        });

You seem to know the exact node to load, in which case you don’t need equalTo. Instead, you can find the node in the following way:

Query presidentquery = mDatabase.child("validate").child(uid).child("President");

The rest of your code can remain unchanged.