= polymorphic_identity

polymorphic_identity dynamically generates aliases for polymorphic associations
based on the class names of those associations.

== Resources

Wiki

* http://wiki.pluginaweek.org/Polymorphic_Identity

Announcement

* http://www.pluginaweek.org/2007/02/12/12-models-seek-damages-for-identity-theft

Source

* http://svn.pluginaweek.org/trunk/plugins/active_record/associations/polymorphic_identity

Development

* http://dev.pluginaweek.org/browser/trunk/plugins/active_record/associations/polymorphic_identity

== Description

Polymorphic associations are not very descriptive when it comes to easily
knowing the type of model your interacting with.  For example, a typical
polymorphic assocation looks like the following:

  class Tag < ActiveRecord::Base
    belongs_to :taggable,
                 :polymorphic => true
  end

When getting the taggable record, you would normally have to called
+tag.taggable+.  However, if you know that the taggable record is just an
instance of the Article model, then it would feel more comfortable if you could
just called +tag.article+.  polymoprhic_identity makes this possible by
dynamically checking the name of the polymorphic record's class and creating
methods that allow you to access the polymorphic association based on that
class name.

== Example

  class Comment < ActiveRecord::Base
    belongs_to :commentable,
                 :polymorphic => true
    belongs_to :commenter,
                 :polymorphic => true
  end
  
  class Article < ActiveRecord::Base
    has_many :comments, :as => :commentable
  end
  
  class User < ActiveRecord::Base
    has_many :comments,
               :as => :commenter
  end
  
  >> c = Comment.find(1)
  => #<Tag:0xb784d32c @attributes={"id"=>"1", "commentable_type"=>"Article", "commentable_id"=>"1", "commenter_type"=>"User", "commenter_id"=>"1"}>
  >> c.commentable
  => #<Article:0xb779d5a8 @attributes={"id"=>"1"}>
  >> c.article
  => #<Article:0xb779d5a8 @attributes={"id"=>"1"}>
  >> c.commenter
  => #<User:0xb775d764 @attributes={"id"=>"1"}>
  >> c.user
  => #<User:0xb775d764 @attributes={"id"=>"1"}>