ActiveRecord::Relation#merge example

gistfile1.rb

class Edition < ActiveRecord::Base
  scope :published, where(arel_table[:published_at].not_eq(nil))
  scope :generated, where(arel_table[:generated_at].not_eq(nil))
  scope :available, published.generated
end

class Magazine < ActiveRecord::Base
  # This is where #merge works its magic, by allowing you to merge scopes from other models.
  scope :with_available_editions, includes(:editions).merge(Edition.available)
end