Firestore query subcollections

Question

I thought I read that you can query subcollections with the new Firebase Firestore, but I don\'t see any examples. For example I have my Firestore setup in the following way

Answer 1

It could be better to use a flat data structure.
The docs specify the pros and cons of different data structures on this page.

Specifically about the limitations of structures with sub-collections:

You can't easily delete subcollections, or perform compound queries across subcollections.

Contrasted with the purported advantages of a flat data structure:

Root-level collections offer the most flexibility and scalability, along with powerful querying within each collection.