Return true if a specific sub collection exists in Firebase/Firestore

Question

I want to know if sub collection 'categories' is created inside my users collection in Firestore and return true if created and false if not

Answer 1

Subcollections are not really created. They simply appear to exist as soon as a document is first added to it, and they appear to be removed as soon as the last document is deleted.

If you want to know if a subcollection appears to exist, then all you have to do is query it. If it returns documents, then you know it exists. You can limit the query to 1 document to be efficient about it.