gistfile1.rb

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

class Article < ActiveRecord::Base
  has_many :comments, :as => :commentable
end


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

>> @article = Article.new
@article = Article.new

=> #<Article id: nil, created_at: nil, updated_at: nil>

>> @article.comments.build(:content=>"Hello")
@article.comments.build(:content=>"Hello")

=> #<Comment id: nil, created_at: nil, updated_at: nil, content: "Hello", commentable_id: nil, commentable_type: "Article">

>> @article.save
@article.save

=> true

>> @comment = @article.comments.last
@comment = @article.comments.last

=> #<Comment id: 2, created_at: "2010-04-29 14:54:07", updated_at: "2010-04-29 14:54:07", content: "Hello", commentable_id: 2, commentable_type: "Article">

>> @comment.update_attributes(:commentable_id=>"", :commentable_type=>"")
@comment.update_attributes(:commentable_id=>"", :commentable_type=>"")

=> true

>>