Generate polymorphic url

Imagine that we have three models, Post, News and Comment. It's common that a post has many comments and a news has many comments, so we define them as

class Post < ActiveRecord::Base
  has_many :comments
end
class News < ActiveRecord::Base
  has_many :comments
end
class Comment < ActiveRecord::Base
  belongs_to :commentable, :polymorphic => true
end

And we define the routes here

resources :posts do
  resources :comments
end
resources :news do
  resources :comments
end

What if you want to generate the url for posts' comments and news' comments?

Bad Smell

this is the common way to get the url for post's comments and news' comments

# parent may be a post or a news
if Post === parent
  post_comments_path(parent)
elsif News === parent
  news_comments_path(parent)
end

this can get the url for post and news

if Post === parent
  post_path(parent)
elsif News === parent
  news_path(parent)
end

Refactor

Rails provides a simple way to generate the polymorphic url.

So we can use the polymorphic_path to get the url for post's comments and news' comments

polymorphic_path([parent, Comment])    # "/posts/1/comments" or "'news/1/comments"

and this can get the url for post and news

polymorphic_path(parent)    # "http://example.com/posts/1/comments" or "http://example.com/news/1/comments"

polymorphic_path makes polymorphic url generation much easier and simpler. There is also a method named polymorphic_url which is the same as the polymorphic_path except that polymorphic_url generate the full url including the host name.

Besides these, rails also provides the new and edit action for polymorphic_path/polymorphic_url

new_polymorphic_path(Post)    # "/posts/new"
new_polymorphic_url(Post)    # "http://example.com/posts/new"
edit_polymorphic_path(post)    # "/posts/1/edit"
edit_polymorphic_url(post)    # "http://example.com/posts/1/edit"