1. Understand the use of scope and namespace in routes.rb.
2. Create a module scoped controller.

We're going to explore different ways of routing things in our blog application to help us organize and group certain routes and controllers more logically.

We decide that we want to keep track of some basic blog statistics, such as how many posts and authors we have. We start by creating a stats_controller.rb with an index action and corresponding view.

We can't actually browse to it yet because we need to set up a route. Let's add it to routes.rb:

# config/routes.rb

get '/stats', to: 'stats#index'

Easy enough, but, after thinking about it, /stats isn't something we want to just hang off the root of our blog URL for anyone to see. It's really just for blog admins, and we want to set up a URL scheme to segregate admin things into their own logical space.

We modify our route:

# config/routes.rb

get '/admin/stats', to: 'stats#index'

Now we can browse to /admin/stats for the stats page, and we can no longer go straight to /stats.

Over time, we might decide to add more admin functions, grouping them all together like we did above, until eventually our routes.rb looks something like this:

# config/routes.rb

...

get '/admin/stats', to: 'stats#index'
get '/admin/authors/new', to: 'authors#new'
get '/admin/authors/delete', to: 'authors#delete'
get '/admin/authors/create', to: 'authors#create'
get '/admin/comments/moderate', to: 'comments#moderate'

As you can see, even with only a few more actions in our admin section, our routes are getting ugly. Not to mention we're repeating ourselves a lot by typing in /admin on all these routes. Yes, even routes should be DRY!

What we need is a way to group all these under /admin without typing /admin all the time. That's where scope comes in.

In routing, scope allows us to prefix a block of routes under one grouping. So let's change our stats route:

# config\routes.rb

scope '/admin' do
  resources :stats, only: [:index]
end

Now we can reload /admin/stats, and it still works. Notice our new route is resourced. Now that we don't have to manually prefix /admin, we can go back to using resourced routes within the /admin scope.

If you run rake routes, you'll see that the new /admin/stats helpers are stats_path and stats_url.

Scoping works nicely to group our URLs together logically, but what happens when we have a bunch of controllers that are handling admin functions? As the application grows, it's going to be harder and harder to keep track of which controllers are for regular blog functions and which are for admin functions.

We want to group all our admin controllers logically to make it easier to maintain and add to the app, so let's add an /admin directory under /controllers where all the admin controllers will go:

mkdir app/controllers/admin

Now let's move our stats_controller.rb into the /admin folder:

mv app/controllers/stats_controller.rb app/controllers/admin

When you create a new folder under /controllers, Rails will automatically pick that up as a module and expect you to namespace the controller accordingly. We need to modify our admin/stats_controller.rb to look like this:

# controllers/admin/stats_controller.rb

class Admin::StatsController < ApplicationController
  def index

    ...

  end
end

Now that we have our controller in a module, Rails will expect the views to match. Let's create a new directory at /app/views/admin/stats and move our stats/index.html.erb into it, so we'll wind up with /app/views/admin/stats/index.html.erb.

Top-tip: The views folder for a controller module (in this case /admin) expects a subfolder structure that matches the names of the controllers (in this case /admin/stats).

If we try to reload /admin/stats now, we will get an error because we need to tell our routes about our new module.

# config/routes.rb

scope '/admin', module: 'admin' do
  resources :stats, only: [:index]
end

We're telling scope that we want to use /admin as a URL prefix, and we're also letting Rails know that all of the included routes will be handled by controllers in the admin module.

If we reload /admin/stats, everything should work just like it did, but now we are logically organizing our controllers.

Right now, our route is scoped as scope '/admin', module: 'admin', which is fine but perhaps a bit less DRY than we'd like.

Fortunately, Rails gives us a shortcut here. When we want to route with a module and use that module's name as the URL prefix, we can use the namespace method instead of scope, module.

# config/routes.rb

namespace :admin do
  resources :stats, only: [:index]
end

If we reload /admin/stats, everything still works, but we've simplified the declaration of the routes. The namespace method makes the assumption that the path prefix and module name match, saving us some typing.

Top-tip: There is one important difference between scope '/admin', module: 'admin' and namespace :admin, and it's in the URL helpers. Remember above that using scope gave us a stats_path helper. But now that we are using namespace, run rake routes again. You'll see that the helper is now prefixed with admin_, so stats_path becomes admin_stats_path. If you switch from scope to namespace, take care to update any URL helpers you have in use!

We learned how to organize our URLs by using scope to group them with an /admin prefix; how to further organize our controllers using directories and modules; and how to use scope, module or namespace in our routes.