creating a child inside a child in firebase

I have a Realtime Database that has the values of a group code. I want that the codes will be like a firebase of its own, including bitmaps of images, something like that:

,

how can I do that?

I tried to do:

databaseReference.child("CODES").child(groupCode).child(bitMapToString(mBitmap)).setValue(mBitmap);

and

databaseReference.child("CODES").child(groupCode).setValue(mBitmap);

but neither of those work

    {
        String groupCode=this.getArguments().getString("groupNum");
        super.onActivityResult(requestCode, resultCode, data);
        if (resultCode == Activity.RESULT_OK)
        {





                    Uri chosenImageUri = data.getData();

                    Bitmap mBitmap = null;
                    try {
                       mBitmap = MediaStore.Images.Media.getBitmap(requireActivity().getContentResolver(), chosenImageUri);
                       Map<String, Object> codes = new HashMap<>();
                        codes.put(bitMapToString(mBitmap), true);

                        DatabaseReference db=FirebaseDatabase.getInstance().getReference();
                        DatabaseReference groupCodeRef = db.child("CODES").child(groupCode);
                        groupCodeRef.setValue(codes);

this is the code i have, and it just doesnt work. if i remove the part from the map until the end it will work, so the problem is in the insertion

this is bitMapToString:

        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        bitmap.compress(Bitmap.CompressFormat.PNG, 100, baos);
        byte[] b = baos.toByteArray();
        String temp = Base64.encodeToString(b, Base64.DEFAULT);
        return temp;
    }

If you want to store multiple values under the 41947781 node, then you have to add key-values pairs right under it. To achieve that using Java, please check the code below:

Map<String, Object> codes = new HashMap<>();
codes.put("bitmap1", true);
codes.put("bitmap2", true);
codes.put("bitmap3", true);

DatabaseReference db = FirebaseDatabase.getInstance().getReference();
DatabaseReference groupCodeRef = db.child("CODES").child(groupCode);
groupCodeRef.setValue(codes);

I also recommend you attach a listener to the setValue() operation, to see if something goes wrong.

The above code will create a structure that looks like this:

db
|
--- CODES
     |
     --- 41947781
           |
           --- bitmap1: true
           |
           --- bitmap2: true
           |
           --- bitmap3: true

It's true we could add the codes into an array rather then in a map, but I recommend you read the following resource:

• Best Practices: Arrays in Firebase