polymorphic_identity dynamically generates aliases for polymorphic associations based on the class names of those associations.
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 call 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 call 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.
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 id: 1, commentable_id: 1, commentable_type: "Article", commenter_id: 1, commenter_type: "User"}> c.commentable # => #<Article id: 1> c.article # => #<Article id: 1> c.commenter # => #<User id: 1> c.user # => #<User id: 1>
Before you can run any tests, the following gem must be installed:
To run against a specific version of Rails:
rake test RAILS_FRAMEWORK_ROOT=/path/to/rails
Rails 2.0 or later