Please see wiki for discussion.
The DM polymorphic gem mimics AR style polymorphism. It has been decided that DM will not follow this path, since it
really isn’t very nice on the DB and there are other ways, that do not require DBA to cry to achieve the same result.
That being said this is still useful for those ppl wishing to convert rails apps over.
One Massive Caveat is that using this you will get n+1 calls to the db atm if you do Comments#commentable for example. It needs a proxy object if anyone cares to write one.
This is highly experimental software, use it at your own risk.
class Comment
include DataMapper::Resource
property :id, Serial
property :text, String
belongs_to :commentable, :polymorphic => true
# OR use the old syntax
#
# is :polymorphic, :commentable
#
end
class Post
include DataMapper::Resource
property :id, Serial
property :name, String
has n, :comments, :as => :commentable
# OR use the old syntax
#
# has n, :comments, :polymorphically => :commentable
#
end
class Article
include DataMapper::Resource
property :id, Serial
property :name, String
has n, :comments, :as => :commentable
# OR use the old syntax
#
# has n, :comments, :polymorphically => :commentable
#
end
This will then provide the following methods
Comment#commentable Comment#post Comment#article Post#comments Article#comments
article = Article.create post = Post.create c1 = Comment.new c2 = Comment.new post.comments << c1 post.save article.comments << c2 article.save c1.commentable # => post c2.commentable # => article c1.post # => post c1.article # => nil c2.post # => nil c2.article # => article post.comments # => [c1] article.comments # => [c2]
no n+1 problem anymore