How does .all() work on select_related in Django?

Question

Django

Hello, I'm learning about the set.all() function, I can't catch up with how it is formed. Let's say I get records from a category

category = Category.objects.select_related().get(id=id)

and pass them to a variable
books = category.book_set.all()
here the question is, how is set.all() formed? where does the book attribute come from in the books_set code?
Thanks for the help.

Answer 1

where does the book attribute come from in the books_set code?

There is a Book model, hence book_set