An example of mixins in Rails

readme.md

With this you can do

Restaurant.all_with_photo #=> will return all the restaurants with a photo
User.first.photo_width #=> 65px
Restaurant.first.photo_url #=> "http://......"

restaurant.rb

class Restaurant < ActiveRecord::Base
  include WithPhoto
end

user.rb

class User < ActiveRecord::Base
  include WithPhoto
end

with_photo.rb

module WithPhoto
  def self.included(base)
    base.send :extend, ClassMethods
    base.send :include, InstanceMethods
  end

  module ClassMethods
    # this is where you have to write all your static methods
    def all_with_photo
      # retrive all the instances with a photo
    end
  end

  module InstanceMethods
    # this is where you write your instance methods
    def photo_url
      #retrive the url for the photo
    end

    def photo_width
      ####
    end

    def photo_height
      ####
    end
  end

end