Firebase Database - the “Fan Out” technique

Question

I was investigating the Firebase Database sample for Android and realized that it stores its data in the following way:

I am not quite familiar with NoSQL t

Answer 1

In my opinion this is not a good approach since you need to keep in sync those data and Firebase doesn't provide any tool to keep duplicates in sync. A good approach would be to store only the key in user-posts.

I suggest reading this, it is very interesting to understand how to structure data: https://www.firebase.com/docs/web/guide/structuring-data.html