scope - Finding records with no associated records in rails 3

Question

class Person < ActiveRecord::Base
  has_many :pets

  scope :with_dog, join(:pets).where("pets.type = 'Dog'")
  scope :without_pets ???????????????????????????????????
end

class Pet < ActiveRecord::Base
  belongs_to :people
end

I'd like to add a scope to the Person model that returns people who have no pets. Any ideas? I feel like this is obvious, but it's escaping me at the moment.

Answer 1

scope :without_pets, lambda { includes(:pets).where('pets.id' => nil) }