ruby-on-railsform-fornested-resources

form_for with nested resources


I have a two-part question about form_for and nested resources. Let's say I'm writing a blog engine and I want to relate a comment to an article. I've defined a nested resource as follows:

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

The comment form is in the show.html.erb view for articles, underneath the article itself, for instance like this:

<%= render :partial => "articles/article" %>
<% form_for([ :article, @comment]) do |f| %>
    <%= f.text_area :text %>
    <%= submit_tag "Submit" %>
<%  end %>

This gives an error, "Called id for nil, which would mistakenly etc." I've also tried

<% form_for @article, @comment do |f| %>

Which renders correctly but relates f.text_area to the article's 'text' field instead of the comment's, and presents the html for the article.text attribute in that text area. So I seem to have this wrong as well. What I want is a form whose 'submit' will call the create action on CommentsController, with an article_id in the params, for instance a post request to /articles/1/comments.

The second part to my question is, what's the best way to create the comment instance to begin with? I'm creating a @comment in the show action of the ArticlesController, so a comment object will be in scope for the form_for helper. Then in the create action of the CommentsController, I create new @comment using the params passed in from the form_for.

Thanks!


Solution

  • 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.