scope_example_for_savage.rb

Item.with_extended_attributes.order("created_at")

class Item < ActiveRecord::Base
  has_one :car_attributes
  has_one :dvd_attributes

  def self.with_extended_attributes
    #you could use some association introspection to build the list of includes
    associations = [:dvd_attributes, :car_attributes]
    includes(associations.map{|i| "LEFT JOIN #{i} ON items.id = #{i.to_s.tableize}.id"}.join(" "))
  end
end