我是否需要检查 Rails 中的belongs_to 关联中是否存在记录？

Question

This might be a silly question, but I would like to know if it's a good practice to test if a record exists, even when is a 'belongs_to' association?

For example:

class MyModel < ApplicationRecord
   belongs_to :book

   def my_method
      if self.book.present? # <- Do I need this?
         # Do Something
      end
   end
end

What do you guys think? What about when belongs_to :book, optional: true?

Answer 1

It depends, if having the book is mandatory then obviously you don't need to check for the existence of the association. But if it is not it is a good practice to check or else it might throw an exception when you try to fetch any attribute or make any change on the association. With mandatory I mean this validation:

validates :book, presence: true

Or having a NOT NULL constraint on the database column or having:

belongs_to :book

without optional: true

Also instead of self.book.present? you could check book_id.present? or book.present? . Two things here:

1. self is redundant, it is not required
2. If you just want to check the association exists or not and don't want to load that from the database you could check book_id.present