Customizing the Rails Index Action

2013.09.15

Assume we have a list of blog posts. The corresponding controller might look like the following:

class PostsController < ApplicationController
  def index
    @posts = Post.all.entries
  end

  # ... other restful actions
end

The routes file would likewise be fairly straightforward:

MyCoolBlog::Application.routes.draw do
  resources :posts
end

Everything is fine and well, and completely RESTful. So what happens when we want to introduce an archive feature and provide a route to show all the archived posts?

Let’s try to make our index method smarter. If we have a link to our archived posts somehwere on our site, we could just pass in an archived=true parameter in the get request.

# in some ERB template linking to the archived posts
<%= link_to "Archived Posts", posts_path(archived: true) %>

This will create the following URL:

/posts?archived=true

From there, in the index action, we could simply branch on the presence of this parameter.

class PostsController < ApplicationController
  def index
    if params[:archived] && params[:archived] == true
      @posts = Post.where(archived: true).entries
    else
      @posts = Post.all.entries
    end
  end
end

The code above works, but leaves something to be desired. So how can we improve it?

Enter collection routes. If we return to our routes file, and create a new collection under the :posts resources, we’ll have the desired behavior without the hacky feeling.

MyCoolBlog::Application.routes.draw do
  resources :posts do
    collection do
      get :archived
    end
  end
end

By using the above formulation, we now have an archived_posts_path helper method. The next step is to update our controller:

class PostsController < ApplicationController
  def index
    @posts = Post.where(archived: false).entries
  end

  def archived
    @posts = Post.where(archived: true).entries
    render action: :index
  end
end

And voila, we now can create the following link in our ERB template:

<%= link_to "Archived Posts", archived_posts_path %>

The link will generate the following URL: /posts/archived. And Rails will route the request to our archived method in the Posts controller which still uses the same template for our regular index.