form_for with nested resources

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Travis R is correct. (I wish I could upvote ya.) I just got this working myself. With these routes:

resources :articles do
  resources :comments
end

You get paths like:

/articles/42
/articles/42/comments/99

routed to controllers at

app/controllers/articles_controller.rb
app/controllers/comments_controller.rb

just as it says at http://guides.rubyonrails.org/routing.html#nested-resources, with no special namespaces.

But partials and forms become tricky. Note the square brackets:

<%= form_for [@article, @comment] do |f| %>

Most important, if you want a URI, you may need something like this:

article_comment_path(@article, @comment)

Alternatively:

[@article, @comment]

as described at http://edgeguides.rubyonrails.org/routing.html#creating-paths-and-urls-from-objects

For example, inside a collections partial with comment_item supplied for iteration,

<%= link_to "delete", article_comment_path(@article, comment_item),
      :method => :delete, :confirm => "Really?" %>

What jamuraa says may work in the context of Article, but it did not work for me in various other ways.

There is a lot of discussion related to nested resources, e.g. http://weblog.jamisbuck.org/2007/2/5/nesting-resources

Interestingly, I just learned that most people’s unit-tests are not actually testing all paths. When people follow jamisbuck’s suggestion, they end up with two ways to get at nested resources. Their unit-tests will generally get/post to the simplest:

# POST /comments
post :create, :comment => {:article_id=>42, ...}

In order to test the route that they may prefer, they need to do it this way:

# POST /articles/42/comments
post :create, :article_id => 42, :comment => {...}

I learned this because my unit-tests started failing when I switched from this:

resources :comments
resources :articles do
  resources :comments
end

to this:

resources :comments, :only => [:destroy, :show, :edit, :update]
resources :articles do
  resources :comments, :only => [:create, :index, :new]
end

I guess it’s ok to have duplicate routes, and to miss a few unit-tests. (Why test? Because even if the user never sees the duplicates, your forms may refer to them, either implicitly or via named routes.) Still, to minimize needless duplication, I recommend this:

resources :comments
resources :articles do
  resources :comments, :only => [:create, :index, :new]
end

Sorry for the long answer. Not many people are aware of the subtleties, I think.

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