Advanced Routing

Learning Goals

• Understand what the resources syntax in routes.rb generates for us.
• Understand what nesting resources in routes.rb generates for us.
• Understand the 5 pieces of information rails routes gives us.
• Use route helpers
• Understand the difference between namespacing and nested resources`

Vocabulary

• routes
• route helper
• namespace

Set Up

For part of this lesson we’ll use the advanced-routing branch of the Set List Tutorial here.

Warm Up

In your notebook, without using your computer, fill in the following table for the 8 ReSTful routes for a generic “resource”

Include the following for each:

• Verb
• URI Pattern
• Controller#Action

Rails Resources

Rails gives us a handy shortcut for generating the 8 ReSTful routes in our routes.rb file. Open up any Rails app, such as SetList, and add the following line anywhere in your routes file:

config/routes.rb

resources :dogs

Run rails routes -c dogs from the command line. The -c stands for controller, so it will only show you routes for the dogs.

With a partner, explore what this output gives you.

Only/Except

You never want to create routes that you haven’t implemented in your code. If you have resources :dogs in your routes file, but you haven’t implemented the DogsController#destroy action, you would be exposing an unused route. Instead, we give our resource an only option to explicitly say which ReSTful routes we want created. For example, if we only wanted the dogs index, new, and create actions, we could put this in our routes file.

config/routes.rb

resources :dogs, only: [:index, :new, :create]

You can also use except, which will generate the 8 ReSTful routes except the ones specified.

config/routes.rb

resources :dogs, except: [:destroy]

This would be the same as:

config/routes.rb

resources :dogs, only: [:index, :show, :new, :create, :edit, :update]

Note: Generally its better to use only and not except because it’s easier to think in terms of positive rather than negative, and it’s preferred to use only instead of except even if it results in longer code.

With a partner, refactor some of the ReSTful routes in SetList to use the resources syntax.

Nested Resources

Some resources are logically dependent on other resources. In SetList, Songs can’t exist without an Artist.

If we look in our routes for SetList, we’ll see:

get "/artists/:artist_id/songs/new", to: "songs#new"

When we want to make a new song, we need to know which artist we are making the song for. We can also accomplish this with the resources syntax by nesting with a do block:

resources :artists do
  resources :songs
end

This will generate 8 ReSTful routes for artists and 8 ReSTful routes for songs that are nested under an artist. You can also use only/except for nested resources:

resources :artists, only: [:show] do
  resources :songs, only: [:edit]
end

Just like before, we only want to create the routes we need.

With a partner, refactor the nested routes in SetList to use the resources syntax.

What’s the difference between Nested Resources and Namespacing?

Namespacing a route is an organizational tool that helps us categorize routes. Take a look at this routes file:

	    resources :songs, only: [:index]
	    namespace :admin do
	      resources :songs, only: [:index, :show]
	    end

While this might look similar to nested resources, the routes it will produce are different. The paths listed under namespace will have /admin/ tacked on the beginning of them, but admin itself is not a resource. It does not map to a database table like artists and it does not have associated IDs. In this case, prepending the routes with admin is purely for organization and categorization. Using namespacing is akin to putting existing routes in a folder called admin. Take a look at what rails routes will output for these routes.

         Prefix 	Verb   	URI Pattern                	Controller#Action
           songs 	GET    	/songs(.:format)            songs#index
     admin_songs 	GET  		/admin/songs(.:format)      admin/songs#index
			admin_song 	GET    	/admin/songs/:id(.:format) 	admin/songs#show

When creating a controller for actions that come from namespaced routes, it’s conventional to declare the namespace title as a module, like so:

class Admin::SongsController < ApplicationController

The path for the above controller in the application’s file directory would likely be controllers/admin/songs_controller.rb. Note the admin sub-directory.

Route Helpers

If you run rails routes, you’ll notice the first column is called “prefix”. Rails will use the “prefix” column to build route helpers.

Route helpers will generate a path for you (note: just the path, not the VERB). All you have to do is append _path to the end of the prefix name. For example, if you have this in your routes:

resources :dogs, only: [:index]

Then rails routes -c dogs should give you:

Prefix Verb URI Pattern     Controller#Action
  dogs GET  /dogs(.:format) dogs#index

Using that prefix dogs we can use dogs_path anywhere in our Rails app to generate the path /dogs.

Generally, any row in your rails routes output that does not include a prefix uses the same prefix as the line above it.

Passing Parameters to Route Helpers

Some paths include parameters. For example:

resources :dogs, only: [:show]

Gives you this rails routes output:

Prefix Verb URI Pattern         Controller#Action
   dog GET  /dogs/:id(.:format) dogs#show

You can’t generate the path using dog_path because it is expecting to be passed an :id. Any time a route helper needs a dynamic parameter like :id, we MUST pass a value to the route helper. For example, dog_path(29) will generate /dogs/29.

We can also pass an object rather than the actual value of the parameter and Rails is smart enough to extract that object’s id. This below, is considered best practice.

journey = Artist.create(name: 'Journey')
visit artist_path(journey)

Be careful. If you forget to pass a parameter to a route helper that needs it, the error message will start to look like a “missing route” error. Read the ENTIRE error, and it will actually tell you that the route helper is missing a parameter.

Partner Practice

Refactor some of the code in setlist to use Route Helpers rather than hardcoded routes.

Checks for Understanding

• What are the 8 ReSTful routes and their controller/actions?
• What routes would resources :dogs, only: [:destroy, :index] generate?
• What routes would the following generate?

resources :owners, only: [:index] do
  resources :dogs, only: [:show]
end

• Why should you use only/except?
• How can you use the prefix column from rails routes?

Completed code can be found on the advanced-routing-complete branch here.