polymorphic_associations_and_modules.rb

# the data model is based on
# http://railscasts.com/episodes/154-polymorphic-association-revised

class Article < ActiveRecord::Base
  has_many :comments, as: :commentable
  
  # example for a custom function that is always the same for each "commentable"
  def most_important_comment
    comments.first
  end
end

class Post < ActiveRecord::Base
  has_many :comments, as: :commentable
  
  # example for a custom function that is always the same for each "commentable"
  def most_important_comment
    comments.first
  end
end

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end


###################

# I would like to group common behaviour, either by inheritance, or via Ruby mixins
# Using Modules
module Commentable
  # this will break saying "has_many" is not defined
  # I can
  # include ActiveRecord::Associations
  # but that will then crash saying "undefined method `dangerous_attribute_method?`"
  has_many :comments, as: :commentable
  
  # example for a custom function that is always the same for each "commentable"
  def most_important_comment
    comments.first
  end
end

class Article
  include Commentable
end

class Post
  include Commentable
end

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
end