Find Missing Relations Easily with .missing

It can be kind of clunky to query ActiveRecord for records where the has_manyassociation is empty.

Say I have an Author class that has many Books. One way to query for Authors without books is the following:

class Author < ApplicationRecord
  has_many :books
end

Author.left_joins(:books).where(books: {id: nil}) 

This totally works, but at least for me is difficult to reason what we're querying. However, Rails 6.1 added a .missing method that really helps clarify what the query is doing:

Author.where.missing(:books)

Much clearer - this will grab all authors that do not have any books.

Docs for further reading. Happy querying!