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Suppose you’re trying to be a good Rails developer and use RESTful routing wherever possible in your application. Using the ever-present blog example¹, you might implement your PostController’s index action like this:

def index
  @posts = Post.all unless request.format.rss?

  respond_to do |format|
    format.html  # render posts.html.erb
    format.xml   { render :xml => @posts }
    format.rss   { @posts = Post.all(:limit => 10, :order => 'created_at desc') }
  end
end

In other words, for HTML and XML clients, we return all the posts, formatted accordingly. For RSS readers, we only give out the 10 most recent posts².

Without doing anything special, this url:

/posts.rss

will automatically use /app/views/posts/index.rss.rxml (which we have to write) to generate our RSS data feed.

But I Knew That Already

Ok, but suppose you’re converting an existing site, and your readers already grab your feed at this url:

/posts/feed

Now, our code won’t work. Rails will try to call the show action, using feed as an :id parameter. Not good.

At this point, the easiest thing to do is to add a custom action to your controller:

def feed
  @posts = Post.all(:limit => 10, :order => 'created_at desc')
  # render default template
end

Rails will automatically find a template named, say, app/views/posts/feed.rxml and use it generate the feed.

But those who know me, know that I despise custom actions. Yes, once in a blue moon I have to use them. But in this situation, I prefer to use a more elegant solution: routes.

Ok, But Did You Know How To Do This?

We need to support /posts/feed as our url for RSS feeds. Remember that Rails routing allows us to route any url we want into any controller action we want. So somewhere above the map.resources :posts line in our routes.rb file, we do this³:

  map.feed 'posts/feed', :controller => 'posts', :format => 'rss'

And now if you go to /posts/feed, your glorious index action will be called and will respond as if an RSS client has made the request.

Cool, no?

¹ At our workshop, we will build something more interesting than a blog.

² We’ll also learn how to use named scopes to simplify this kind of code.

³ Even in development mode, you might have to restart your local server (mongrel or webrick or thin or whatever) to get Rails to pickup your routing changes.

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