Scopes for belongs_to?

Question

Ruby on Rails

there is an example in the Rails Guides documentation

class Book < ApplicationRecord
  belongs_to :author, -> { where active: true }
end

Can you please explain what this part is?
:author, -> { where active: true }

Answer 1

The construction means that when association with model membership is performed, a closure (lambda, or just an anonymous method) will be performed, inside which records of authors of books and , whose active property is true, are filtered. In other words: Thus, when searching for a book, RoR will add the rest of the association with the book itself by performing an SQL INNER JOIN between the two tables.
-> { where active: true }:author