Rails: Nested resources conflict, how to scope the index action depending on the called route

Question

Imagine you have two defined routes:

map.resources articles
map.resources categories, :has_many => :articles

both accessible by helpers/paths

articles_path # /articles
category_articles_path(1) # /category/1/articles

if you visit /articles, index action from ArticlesController is executed.

if you visit /category/1/articles, index action from ArticlesController is executed too.

So, what is the best approach for conditionally selecting only the scoped articles depending on the calling route?

#if coming from the nested resource route
@articles = Articles.find_by_category_id(params[:category_id])
#else
@articles = Articles.all

Answer 1

You have two choices here, depending on how much your logic and your view is tied to the scope. Let me explain further.

The first choice is to determine the scope within your controller, as already explained by the other responses. I usually set a @scope variable to get some additional benefits in my templates.

class Articles

  before_filter :determine_scope

  def index
    @articles = @scope.all
    # ...
  end

  protected

    def determine_scope
      @scope = if params[:category_id]
        Category.find(params[:category_id]).articles
      else
        Article
      end
    end

end

The reason for the @scope variable is that you might need to know the scope of your request outside the single action. Let's assume you want to display the number of records in your view. You need to know whether you are filtering by category or not. In this case, you simply need to call @scope.count or @scope.my_named_scope.count instead of repeating each time the check on params[:category_id].

This approach works well if your views, the one with category and the one without category, are quite similar. But what happens when the listing filtered by category is completely different compared to the one without a category? This happens quite often: your category section provides some category-focused widgets while your article section some article-related widgets and filter. Also, your Article controller has some special before_filters you might want to use, but you don't have to use them when the article listing belongs to a category.

In this case, you might want to separate the actions.

map.resources articles
map.resources categories, :collection => { :articles => :get }

articles_path # /articles and ArticlesController#index
category_articles_path(1) # /category/1/articles and CategoriesController#articles

Now the listing filtered by category is managed by the CategoriesController and it inherits all the controller filters, layouts, settings... while the unfiltered listing is managed by the ArticlesController.

This is usually my favorite choice because with an additional action you don't have to clutter your views and controllers with tons of conditional checks.

Answer 2

I often like to separate those actions. When the resulting actions are very similar you can separate the scopes inside the controller easy by seeing if params[:category_id] is present etc (see @SimoneCarletti answer).

Normally separating actions in the controller by using custom routes gives you most flexibility and clear results. Following code results in normal route helper names but the routes are directed to specific actions in controller.

In routes.rb:

resources categories do
  resources articles, :except => [:index] do
    get :index, :on => :collection, :action => 'index_articles'
  end
end
resources articles, :except => [:index] do
  get :index, :on => :collection, :action => 'index_all'
end

Then you can have in ArticlesController.rb

def index_all
  @articles = @articles = Articles.all
  render :index # or something else
end

def index_categories
  @articles = Articles.find_by_category_id(params[:category_id])
  render :index # or something else
end

Answer 3

Having only a single nested resource, using a conditional based on the params to determine it's scope would be the easiest approach. This is likely the way to go in your case.

if params[:category_id]
  @articles = Category.find(params[:category_id]).articles
else
  @articles = Article.all
end

However, depending on what other nested resources you have for the model, sticking with this approach can get quite tedious. In which case, using a plugin like resource_controller or make_resourceful will make this much simpler.

class ArticlesController < ResourceController::Base
  belongs_to :category
end

This will actually do everything you'd expect. It gives you all your standard RESTful actions and will automatically setup the scope for /categories/1/articles.

Answer 4

if params[:category_id].blank?
  # all
else
  # find by category_id
end

I like to consider the action independent from the route. No matter how they get there, make a reasonable decision as to what to do.