Ruby on Rails: Restful Links When You Don’t Know the Class

I had a friend email me a week or so ago about generating a link from your restful routes when you don’t know the class. Here’s a quick thumbnail of the scenario.

You have a bunch of restful routes like these:

map.resources :users
map.resources :groups

And you have a model that has a polymorphic association, meaning that it has an associated value that can be from more than one model. Here’s an example of how that’s done.

class Post  true
end

class User   wner
end

class Group
  has_many :posts, :as =>  wner
end

Now, let’s say that when you show a post, you want to provide a link to the owner of the post when you display it on its show page. You know that because you’ve provided the restful routes in your config/routes.rb file as show above, you get the nice functionality of the user_path and the group_path methods. The problem is that because you don’t know if @post.owner is a user or a group.

You could conditionally call one of the methods:

That’s a little messy, but it works. The solution I suggested was a little more elegant, but still a little messy:

It removed the conditionals, but it’s not very clear to read. It turns out that he found a solution already baked into Ruby on Rails:

You can find documentation on the polymorphic_path method on RailsBrain.

You’ll find that polymorphic_path also supports other forms of the path helpers such as edit_polymorphic_path, new_polymorphic_path, and formatted_polymorphic_path.

I also got information from railspikes.com.