[radicalism]

It would return the same value, but the approach to obtain it would be different.

`user` would be a property defined as a User object on the Book model, so accessing `book.user` will cause the framework to fetch the entire user model (even if we then only fetch the id).

On the other hand, `book.user_id` is the auto-generated database column, generated to make the above property definition possible. But since this `user_id` is directly defined on the book object, there is no need to query the user table.