Get Value From Realtime Firebase Inside Child

Greeting everyone, im working a project right now and need help for firebase realtime database.

My firebase Project

As you guys can see in the above picture, inside student, I have matric number, and inside matric number have block and department.

I have a barcode scanner which scan the value of department and return to get the matric number. Any solution.

Below code is my progress.

mCodeScanner.setDecodeCallback(new DecodeCallback() {
        @Override
        public void onDecoded(@NonNull final Result result) {
            runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    r = result.getText();
                    Query s = ref.equalTo("JTMK", "department");
                    name.setText(r);
        }});}});

Answer

If you don’t know the matric number of the student, indeed a query is required. Assuming that result.getText() returns JTMK, please use the following lines of code:

mCodeScanner.setDecodeCallback(new DecodeCallback() {
    @Override
    public void onDecoded(@NonNull final Result result) {
        String department = result.getText();
        DatabaseReference db = FirebaseDatabase.getInstance().getReference();
        DatabaseReference studentRef = db.child("Student");
        Query queryByDepartment = studentRef.orderByChild("department").equalTo(department).limitToFirst(1);
        queryByDepartment.get().addOnCompleteListener(new OnCompleteListener<DataSnapshot>() {
            @Override
            public void onComplete(@NonNull Task<DataSnapshot> task) {
                if (task.isSuccessful()) {
                    for (DataSnapshot ds : task.getResult().getChildren()) {
                        String block = ds.child("block").getValue(String.class);
                        name.setText(block);
                        Log.d("TAG", block);
                    }
                } else {
                    Log.d("TAG", task.getException().getMessage()); //Never ignore potential errors!
                }
            }
        });
    }
});

Things to notice:

1. There is no need to use runOnUiThread when reading data from the Realtime Database.
2. Firebase API is asynchronous. So I recommend you read the following resource:
   • How to read data from Firebase Realtime Database using get()?
3. When you run the code, you should see in the logcat BESTARI 4, which will also be set to name TextView.