Sometimes, in certain circumstances, it is reasonable to have a foreign key value of null.
.has_many method has an argument to set the foreign key column on referencing rows to null when that record is deleted.
class Post < ApplicationRecord belongs_to :author belongs_to :category end class Category < ApplicationRecord has_many :posts, dependent: :nullify end
In this example whenever a category is deleted, any posts referencing the
categories table will have their foreign key set to null.