Needless deep nesting

Bad Smell

map.resources :posts do |post|
  post.resources :comments do |comment|
    comment.resources :favorites
  end
end

<%= link_to post_comment_favorite_path(@post, @comment, @favorite) %>

Is it really necessary to define the 3-level nested routes? Using nested routes means the nested resources is belongs to the parent resources, as example, the resources comments belong to post. But there is no need to define the resources favorites belong to post, because favorites belong to comment.

And deep level nested routes generate too long and verbose urls.

Refactor

map.resources :post do |post|
  post.resources :comments
end

map.resources :comments do |comment|
  comment.resources :favorites
end

<%= link_to comment_favorite_path(@comment, @favorite) %>

So we refactor the 3-level nested routes to two 2-level nested routes. And our urls for favorites are shorter now.

Updated by @flyerhzm

I have learned a new way to solve the needless deep nesting issue.

Refactor 2

map.resources :posts, :shallow => true do |post|
  post.resources :comments do |comment|
    comment.resources :favorites
  end
end

<%= link_to comment_favorite_path(@comment, @favorite) %>

As you seen, I add shallow => true option to the posts route, it will generate all the nested routes only 1-level or 2-level. The following is the routes it generates.

               posts GET    /posts(.:format)                                  {:action=>"index", :controller=>"posts"}
                     POST   /posts(.:format)                                  {:action=>"create", :controller=>"posts"}
            new_post GET    /posts/new(.:format)                              {:action=>"new", :controller=>"posts"}
           edit_post GET    /posts/:id/edit(.:format)                         {:action=>"edit", :controller=>"posts"}
                post GET    /posts/:id(.:format)                              {:action=>"show", :controller=>"posts"}
                     PUT    /posts/:id(.:format)                              {:action=>"update", :controller=>"posts"}
                     DELETE /posts/:id(.:format)                              {:action=>"destroy", :controller=>"posts"}
       post_comments GET    /posts/:post_id/comments(.:format)                {:action=>"index", :controller=>"comments"}
                     POST   /posts/:post_id/comments(.:format)                {:action=>"create", :controller=>"comments"}
    new_post_comment GET    /posts/:post_id/comments/new(.:format)            {:action=>"new", :controller=>"comments"}
        edit_comment GET    /comments/:id/edit(.:format)                      {:action=>"edit", :controller=>"comments"}
             comment GET    /comments/:id(.:format)                           {:action=>"show", :controller=>"comments"}
                     PUT    /comments/:id(.:format)                           {:action=>"update", :controller=>"comments"}
                     DELETE /comments/:id(.:format)                           {:action=>"destroy", :controller=>"comments"}
   comment_favorites GET    /comments/:comment_id/favorites(.:format)         {:action=>"index", :controller=>"favorites"}
                     POST   /comments/:comment_id/favorites(.:format)         {:action=>"create", :controller=>"favorites"}
new_comment_favorite GET    /comments/:comment_id/favorites/new(.:format)     {:action=>"new", :controller=>"favorites"}
       edit_favorite GET    /favorites/:id/edit(.:format)                     {:action=>"edit", :controller=>"favorites"}
            favorite GET    /favorites/:id(.:format)                          {:action=>"show", :controller=>"favorites"}
                     PUT    /favorites/:id(.:format)                          {:action=>"update", :controller=>"favorites"}
                     DELETE /favorites/:id(.:format)                          {:action=>"destroy", :controller=>"favorites"}

:shallow looks like a better solution, with it, you can use

post_comment_path(1, 1)
comment_path(1)
comment_favorite_path(1, 1)
favorite_path(1)

Awesome, but it's unlucky that the rails document doesn't mention it.