Nested calls, this way is correct?

[padrecedano]

Thanks for this tool. It is very useful especially for those of us who have little knowledge of RXJava.

In my case I need to make nested calls: read a first document where I have the reference to another document.

I am doing it like this:

    FirebaseFirestore firestore = FirebaseFirestore.getInstance();
    DocumentReference parentRef = firestore.document("path/to/parent/document");

    RxFirestore.observeDocumentRef(parentRef)
            .subscribe( parentData -> {
                DocumentReference childRef = parentData.getDocumentReference("reference/i/need");

                RxFirestore.observeDocumentRef(childRef)
                        .subscribe( finalData -> {
                            Log.d("bbbb",finalData.toString());
                        });

            });

The code works, in the second observeDocumentRef I can see the Log with the data, but I want to know if this form is correct. I have no knowledge of RXJava and I do not know if making calls like this with this library could give a problem. If not correct, how can I safely make nested calls?