Rails Routing from the Outside In

This guide covers the user-facing features of Rails routing.

After reading this guide, you will know:

• How to interpret the code in routes.rb.
• How to construct your own routes, using either the preferred resourceful style or the match method.
• What parameters to expect an action to receive.
• How to automatically create paths and URLs using route helpers.
• Advanced techniques such as constraints and Rack endpoints.

Chapters

1. The Purpose of the Rails Router
   • Connecting URLs to Code
   • Generating Paths and URLs from Code
2. Resource Routing: the Rails Default
   • Resources on the Web
   • CRUD, Verbs, and Actions
   • Path and URL Helpers
   • Defining Multiple Resources at the Same Time
   • Singular Resources
   • Controller Namespaces and Routing
   • Nested Resources
   • Routing concerns
   • Creating Paths and URLs From Objects
   • Adding More RESTful Actions
3. Non-Resourceful Routes
   • Bound Parameters
   • Dynamic Segments
   • Static Segments
   • The Query String
   • Defining Defaults
   • Naming Routes
   • HTTP Verb Constraints
   • Segment Constraints
   • Request-Based Constraints
   • Advanced Constraints
   • Route Globbing and Wildcard Segments
   • Redirection
   • Routing to Rack Applications
   • Using root
   • Unicode character routes
4. Customizing Resourceful Routes
   • Specifying a Controller to Use
   • Specifying Constraints
   • Overriding the Named Helpers
   • Overriding the new and edit Segments
   • Prefixing the Named Route Helpers
   • Restricting the Routes Created
   • Translated Paths
   • Overriding the Singular Form
   • Using :as in Nested Resources
   • Overriding Named Route Parameters
5. Inspecting and Testing Routes
   • Listing Existing Routes
   • Testing Routes

1 The Purpose of the Rails Router

The Rails router recognizes URLs and dispatches them to a controller's action. It can also generate paths and URLs, avoiding the need to hardcode strings in your views.

1.1 Connecting URLs to Code

When your Rails application receives an incoming request for:

GET /patients/17

it asks the router to match it to a controller action. If the first matching route is:

get '/patients/:id', to: 'patients#show'

the request is dispatched to the patients controller's show action with { id: '17' } in params.

1.2 Generating Paths and URLs from Code

You can also generate paths and URLs. If the route above is modified to be:

get '/patients/:id', to: 'patients#show', as: 'patient'

and your application contains this code in the controller:

@patient = Patient.find(17)

and this in the corresponding view:

<%= link_to 'Patient Record', patient_path(@patient) %>

then the router will generate the path /patients/17. This reduces the brittleness of your view and makes your code easier to understand. Note that the id does not need to be specified in the route helper.

2 Resource Routing: the Rails Default

Resource routing allows you to quickly declare all of the common routes for a given resourceful controller. Instead of declaring separate routes for your index, show, new, edit, create, update and destroy actions, a resourceful route declares them in a single line of code.

2.1 Resources on the Web

Browsers request pages from Rails by making a request for a URL using a specific HTTP method, such as GET, POST, PATCH, PUT and DELETE. Each method is a request to perform an operation on the resource. A resource route maps a number of related requests to actions in a single controller.

When your Rails application receives an incoming request for:

DELETE /photos/17

it asks the router to map it to a controller action. If the first matching route is:

resources :photos

Rails would dispatch that request to the destroy method on the photos controller with { id: '17' } in params.

2.2 CRUD, Verbs, and Actions

In Rails, a resourceful route provides a mapping between HTTP verbs and URLs to controller actions. By convention, each action also maps to particular CRUD operations in a database. A single entry in the routing file, such as:

resources :photos

creates seven different routes in your application, all mapping to the Photos controller:

HTTP Verb	Path	Controller#Action	Used for
GET	/photos	photos#index	display a list of all photos
GET	/photos/new	photos#new	return an HTML form for creating a new photo
POST	/photos	photos#create	create a new photo
GET	/photos/:id	photos#show	display a specific photo
GET	/photos/:id/edit	photos#edit	return an HTML form for editing a photo
PATCH/PUT	/photos/:id	photos#update	update a specific photo
DELETE	/photos/:id	photos#destroy	delete a specific photo

2.3 Path and URL Helpers

Creating a resourceful route will also expose a number of helpers to the controllers in your application. In the case of resources :photos:

• photos_path returns /photos
• new_photo_path returns /photos/new
• edit_photo_path(:id) returns /photos/:id/edit (for instance, edit_photo_path(10) returns /photos/10/edit)
• photo_path(:id) returns /photos/:id (for instance, photo_path(10) returns /photos/10)

Each of these helpers has a corresponding _url helper (such as photos_url) which returns the same path prefixed with the current host, port and path prefix.

2.4 Defining Multiple Resources at the Same Time

If you need to create routes for more than one resource, you can save a bit of typing by defining them all with a single call to resources:

resources :photos, :books, :videos

This works exactly the same as:

resources :photos
resources :books
resources :videos

2.5 Singular Resources

Sometimes, you have a resource that clients always look up without referencing an ID. For example, you would like /profile to always show the profile of the currently logged in user. In this case, you can use a singular resource to map /profile (rather than /profile/:id) to the show action:

get 'profile', to: 'users#show'

Passing a String to get will expect a controller#action format, while passing a Symbol will map directly to an action:

get 'profile', to: :show

This resourceful route:

resource :geocoder

creates six different routes in your application, all mapping to the Geocoders controller:

HTTP Verb	Path	Controller#Action	Used for
GET	/geocoder/new	geocoders#new	return an HTML form for creating the geocoder
POST	/geocoder	geocoders#create	create the new geocoder
GET	/geocoder	geocoders#show	display the one and only geocoder resource
GET	/geocoder/edit	geocoders#edit	return an HTML form for editing the geocoder
PATCH/PUT	/geocoder	geocoders#update	update the one and only geocoder resource
DELETE	/geocoder	geocoders#destroy	delete the geocoder resource

A singular resourceful route generates these helpers:

• new_geocoder_path returns /geocoder/new
• edit_geocoder_path returns /geocoder/edit
• geocoder_path returns /geocoder

As with plural resources, the same helpers ending in _url will also include the host, port and path prefix.

form_for @geocoder, url: geocoder_path do |f|

2.6 Controller Namespaces and Routing

You may wish to organize groups of controllers under a namespace. Most commonly, you might group a number of administrative controllers under an Admin:: namespace. You would place these controllers under the app/controllers/admin directory, and you can group them together in your router:

namespace :admin do
  resources :articles, :comments
end

This will create a number of routes for each of the articles and comments controller. For Admin::ArticlesController, Rails will create:

HTTP Verb	Path	Controller#Action	Named Helper
GET	/admin/articles	admin/articles#index	admin_articles_path
GET	/admin/articles/new	admin/articles#new	new_admin_article_path
POST	/admin/articles	admin/articles#create	admin_articles_path
GET	/admin/articles/:id	admin/articles#show	admin_article_path(:id)
GET	/admin/articles/:id/edit	admin/articles#edit	edit_admin_article_path(:id)
PATCH/PUT	/admin/articles/:id	admin/articles#update	admin_article_path(:id)
DELETE	/admin/articles/:id	admin/articles#destroy	admin_article_path(:id)

If you want to route /articles (without the prefix /admin) to Admin::ArticlesController, you could use:

scope module: 'admin' do
  resources :articles, :comments
end

or, for a single case:

resources :articles, module: 'admin'

If you want to route /admin/articles to ArticlesController (without the Admin:: module prefix), you could use:

scope '/admin' do
  resources :articles, :comments
end

or, for a single case:

resources :articles, path: '/admin/articles'

In each of these cases, the named routes remain the same as if you did not use scope. In the last case, the following paths map to ArticlesController:

HTTP Verb	Path	Controller#Action	Named Helper
GET	/admin/articles	articles#index	articles_path
GET	/admin/articles/new	articles#new	new_article_path
POST	/admin/articles	articles#create	articles_path
GET	/admin/articles/:id	articles#show	article_path(:id)
GET	/admin/articles/:id/edit	articles#edit	edit_article_path(:id)
PATCH/PUT	/admin/articles/:id	articles#update	article_path(:id)
DELETE	/admin/articles/:id	articles#destroy	article_path(:id)

2.7 Nested Resources

It's common to have resources that are logically children of other resources. For example, suppose your application includes these models:

class Magazine < ActiveRecord::Base
  has_many :ads
end

class Ad < ActiveRecord::Base
  belongs_to :magazine
end

Nested routes allow you to capture this relationship in your routing. In this case, you could include this route declaration:

resources :magazines do
  resources :ads
end

In addition to the routes for magazines, this declaration will also route ads to an AdsController. The ad URLs require a magazine:

HTTP Verb	Path	Controller#Action	Used for
GET	/magazines/:magazine_id/ads	ads#index	display a list of all ads for a specific magazine
GET	/magazines/:magazine_id/ads/new	ads#new	return an HTML form for creating a new ad belonging to a specific magazine
POST	/magazines/:magazine_id/ads	ads#create	create a new ad belonging to a specific magazine
GET	/magazines/:magazine_id/ads/:id	ads#show	display a specific ad belonging to a specific magazine
GET	/magazines/:magazine_id/ads/:id/edit	ads#edit	return an HTML form for editing an ad belonging to a specific magazine
PATCH/PUT	/magazines/:magazine_id/ads/:id	ads#update	update a specific ad belonging to a specific magazine
DELETE	/magazines/:magazine_id/ads/:id	ads#destroy	delete a specific ad belonging to a specific magazine

This will also create routing helpers such as magazine_ads_url and edit_magazine_ad_path. These helpers take an instance of Magazine as the first parameter (magazine_ads_url(@magazine)).

2.7.1 Limits to Nesting

You can nest resources within other nested resources if you like. For example:

resources :publishers do
  resources :magazines do
    resources :photos
  end
end

Deeply-nested resources quickly become cumbersome. In this case, for example, the application would recognize paths such as:

/publishers/1/magazines/2/photos/3

The corresponding route helper would be publisher_magazine_photo_url, requiring you to specify objects at all three levels. Indeed, this situation is confusing enough that a popular article by Jamis Buck proposes a rule of thumb for good Rails design:

2.7.2 Shallow Nesting

One way to avoid deep nesting (as recommended above) is to generate the collection actions scoped under the parent, so as to get a sense of the hierarchy, but to not nest the member actions. In other words, to only build routes with the minimal amount of information to uniquely identify the resource, like this:

resources :articles do
  resources :comments, only: [:index, :new, :create]
end
resources :comments, only: [:show, :edit, :update, :destroy]

This idea strikes a balance between descriptive routes and deep nesting. There exists shorthand syntax to achieve just that, via the :shallow option:

resources :articles do
  resources :comments, shallow: true
end

This will generate the exact same routes as the first example. You can also specify the :shallow option in the parent resource, in which case all of the nested resources will be shallow:

resources :articles, shallow: true do
  resources :comments
  resources :quotes
  resources :drafts
end

The shallow method of the DSL creates a scope inside of which every nesting is shallow. This generates the same routes as the previous example:

shallow do
  resources :articles do
    resources :comments
    resources :quotes
    resources :drafts
  end
end

There exist two options for scope to customize shallow routes. :shallow_path prefixes member paths with the specified parameter:

scope shallow_path: "sekret" do
  resources :articles do
    resources :comments, shallow: true
  end
end

The comments resource here will have the following routes generated for it:

HTTP Verb	Path	Controller#Action	Named Helper
GET	/articles/:article_id/comments(.:format)	comments#index	article_comments_path
POST	/articles/:article_id/comments(.:format)	comments#create	article_comments_path
GET	/articles/:article_id/comments/new(.:format)	comments#new	new_article_comment_path
GET	/sekret/comments/:id/edit(.:format)	comments#edit	edit_comment_path
GET	/sekret/comments/:id(.:format)	comments#show	comment_path
PATCH/PUT	/sekret/comments/:id(.:format)	comments#update	comment_path
DELETE	/sekret/comments/:id(.:format)	comments#destroy	comment_path

The :shallow_prefix option adds the specified parameter to the named helpers:

scope shallow_prefix: "sekret" do
  resources :articles do
    resources :comments, shallow: true
  end
end

The comments resource here will have the following routes generated for it:

HTTP Verb	Path	Controller#Action	Named Helper
GET	/articles/:article_id/comments(.:format)	comments#index	article_comments_path
POST	/articles/:article_id/comments(.:format)	comments#create	article_comments_path
GET	/articles/:article_id/comments/new(.:format)	comments#new	new_article_comment_path
GET	/comments/:id/edit(.:format)	comments#edit	edit_sekret_comment_path
GET	/comments/:id(.:format)	comments#show	sekret_comment_path
PATCH/PUT	/comments/:id(.:format)	comments#update	sekret_comment_path
DELETE	/comments/:id(.:format)	comments#destroy	sekret_comment_path

2.8 Routing concerns

Routing Concerns allows you to declare common routes that can be reused inside other resources and routes. To define a concern:

concern :commentable do
  resources :comments
end

concern :image_attachable do
  resources :images, only: :index
end

These concerns can be used in resources to avoid code duplication and share behavior across routes:

resources :messages, concerns: :commentable

resources :articles, concerns: [:commentable, :image_attachable]

The above is equivalent to:

resources :messages do
  resources :comments
end

resources :articles do
  resources :comments
  resources :images, only: :index
end

Also you can use them in any place that you want inside the routes, for example in a scope or namespace call:

namespace :articles do
  concerns :commentable
end

2.9 Creating Paths and URLs From Objects

In addition to using the routing helpers, Rails can also create paths and URLs from an array of parameters. For example, suppose you have this set of routes:

resources :magazines do
  resources :ads
end

When using magazine_ad_path, you can pass in instances of Magazine and Ad instead of the numeric IDs:

<%= link_to 'Ad details', magazine_ad_path(@magazine, @ad) %>

You can also use url_for with a set of objects, and Rails will automatically determine which route you want:

<%= link_to 'Ad details', url_for([@magazine, @ad]) %>

In this case, Rails will see that @magazine is a Magazine and @ad is an Ad and will therefore use the magazine_ad_path helper. In helpers like link_to, you can specify just the object in place of the full url_for call:

<%= link_to 'Ad details', [@magazine, @ad] %>

If you wanted to link to just a magazine:

<%= link_to 'Magazine details', @magazine %>

For other actions, you just need to insert the action name as the first element of the array:

<%= link_to 'Edit Ad', [:edit, @magazine, @ad] %>

This allows you to treat instances of your models as URLs, and is a key advantage to using the resourceful style.

2.10 Adding More RESTful Actions

You are not limited to the seven routes that RESTful routing creates by default. If you like, you may add additional routes that apply to the collection or individual members of the collection.

2.10.1 Adding Member Routes

To add a member route, just add a member block into the resource block:

resources :photos do
  member do
    get 'preview'
  end
end

This will recognize /photos/1/preview with GET, and route to the preview action of PhotosController, with the resource id value passed in params[:id]. It will also create the preview_photo_url and preview_photo_path helpers.

Within the block of member routes, each route name specifies the HTTP verb will be recognized. You can use get, patch, put, post, or delete here . If you don't have multiple member routes, you can also pass :on to a route, eliminating the block:

resources :photos do
  get 'preview', on: :member
end

You can leave out the :on option, this will create the same member route except that the resource id value will be available in params[:photo_id] instead of params[:id].

2.10.2 Adding Collection Routes

To add a route to the collection:

resources :photos do
  collection do
    get 'search'
  end
end

This will enable Rails to recognize paths such as /photos/search with GET, and route to the search action of PhotosController. It will also create the search_photos_url and search_photos_path route helpers.

Just as with member routes, you can pass :on to a route:

resources :photos do
  get 'search', on: :collection
end

2.10.3 Adding Routes for Additional New Actions

To add an alternate new action using the :on shortcut:

resources :comments do
  get 'preview', on: :new
end

This will enable Rails to recognize paths such as /comments/new/preview with GET, and route to the preview action of CommentsController. It will also create the preview_new_comment_url and preview_new_comment_path route helpers.

3 Non-Resourceful Routes

In addition to resource routing, Rails has powerful support for routing arbitrary URLs to actions. Here, you don't get groups of routes automatically generated by resourceful routing. Instead, you set up each route within your application separately.

While you should usually use resourceful routing, there are still many places where the simpler routing is more appropriate. There's no need to try to shoehorn every last piece of your application into a resourceful framework if that's not a good fit.

In particular, simple routing makes it very easy to map legacy URLs to new Rails actions.

3.1 Bound Parameters

When you set up a regular route, you supply a series of symbols that Rails maps to parts of an incoming HTTP request. Two of these symbols are special: :controller maps to the name of a controller in your application, and :action maps to the name of an action within that controller. For example, consider this route:

get ':controller(/:action(/:id))'

If an incoming request of /photos/show/1 is processed by this route (because it hasn't matched any previous route in the file), then the result will be to invoke the show action of the PhotosController, and to make the final parameter "1" available as params[:id]. This route will also route the incoming request of /photos to PhotosController#index, since :action and :id are optional parameters, denoted by parentheses.

3.2 Dynamic Segments

You can set up as many dynamic segments within a regular route as you like. Anything other than :controller or :action will be available to the action as part of params. If you set up this route:

get ':controller/:action/:id/:user_id'

An incoming path of /photos/show/1/2 will be dispatched to the show action of the PhotosController. params[:id] will be "1", and params[:user_id] will be "2".

get ':controller(/:action(/:id))', controller: /admin\/[^\/]+/

3.3 Static Segments

You can specify static segments when creating a route by not prepending a colon to a fragment:

get ':controller/:action/:id/with_user/:user_id'

This route would respond to paths such as /photos/show/1/with_user/2. In this case, params would be { controller: 'photos', action: 'show', id: '1', user_id: '2' }.

3.4 The Query String

The params will also include any parameters from the query string. For example, with this route:

get ':controller/:action/:id'

An incoming path of /photos/show/1?user_id=2 will be dispatched to the show action of the Photos controller. params will be { controller: 'photos', action: 'show', id: '1', user_id: '2' }.

3.5 Defining Defaults

You do not need to explicitly use the :controller and :action symbols within a route. You can supply them as defaults:

get 'photos/:id', to: 'photos#show'

With this route, Rails will match an incoming path of /photos/12 to the show action of PhotosController.

You can also define other defaults in a route by supplying a hash for the :defaults option. This even applies to parameters that you do not specify as dynamic segments. For example:

get 'photos/:id', to: 'photos#show', defaults: { format: 'jpg' }

Rails would match photos/12 to the show action of PhotosController, and set params[:format] to "jpg".

3.6 Naming Routes

You can specify a name for any route using the :as option:

get 'exit', to: 'sessions#destroy', as: :logout

This will create logout_path and logout_url as named helpers in your application. Calling logout_path will return /exit

You can also use this to override routing methods defined by resources, like this:

get ':username', to: 'users#show', as: :user

This will define a user_path method that will be available in controllers, helpers and views that will go to a route such as /bob. Inside the show action of UsersController, params[:username] will contain the username for the user. Change :username in the route definition if you do not want your parameter name to be :username.

3.7 HTTP Verb Constraints

In general, you should use the get, post, put, patch and delete methods to constrain a route to a particular verb. You can use the match method with the :via option to match multiple verbs at once:

match 'photos', to: 'photos#show', via: [:get, :post]

You can match all verbs to a particular route using via: :all:

match 'photos', to: 'photos#show', via: :all

3.8 Segment Constraints

You can use the :constraints option to enforce a format for a dynamic segment:

get 'photos/:id', to: 'photos#show', constraints: { id: /[A-Z]\d{5}/ }

This route would match paths such as /photos/A12345, but not /photos/893. You can more succinctly express the same route this way:

get 'photos/:id', to: 'photos#show', id: /[A-Z]\d{5}/

:constraints takes regular expressions with the restriction that regexp anchors can't be used. For example, the following route will not work:

get '/:id', to: 'articles#show', constraints: { id: /^\d/ }

However, note that you don't need to use anchors because all routes are anchored at the start.

For example, the following routes would allow for articles with to_param values like 1-hello-world that always begin with a number and users with to_param values like david that never begin with a number to share the root namespace:

get '/:id', to: 'articles#show', constraints: { id: /\d.+/ }
get '/:username', to: 'users#show'

3.9 Request-Based Constraints

You can also constrain a route based on any method on the Request object that returns a String.

You specify a request-based constraint the same way that you specify a segment constraint:

get 'photos', to: 'photos#index', constraints: { subdomain: 'admin' }

You can also specify constraints in a block form:

namespace :admin do
  constraints subdomain: 'admin' do
    resources :photos
  end
end

3.10 Advanced Constraints

If you have a more advanced constraint, you can provide an object that responds to matches? that Rails should use. Let's say you wanted to route all users on a blacklist to the BlacklistController. You could do:

class BlacklistConstraint
  def initialize
    @ips = Blacklist.retrieve_ips
  end

  def matches?(request)
    @ips.include?(request.remote_ip)
  end
end

Rails.application.routes.draw do
  get '*path', to: 'blacklist#index',
    constraints: BlacklistConstraint.new
end

You can also specify constraints as a lambda:

Rails.application.routes.draw do
  get '*path', to: 'blacklist#index',
    constraints: lambda { |request| Blacklist.retrieve_ips.include?(request.remote_ip) }
end

Both the matches? method and the lambda gets the request object as an argument.

3.11 Route Globbing and Wildcard Segments

Route globbing is a way to specify that a particular parameter should be matched to all the remaining parts of a route. For example:

get 'photos/*other', to: 'photos#unknown'

This route would match photos/12 or /photos/long/path/to/12, setting params[:other] to "12" or "long/path/to/12". The fragments prefixed with a star are called "wildcard segments".

Wildcard segments can occur anywhere in a route. For example:

get 'books/*section/:title', to: 'books#show'

would match books/some/section/last-words-a-memoir with params[:section] equals 'some/section', and params[:title] equals 'last-words-a-memoir'.

Technically, a route can have even more than one wildcard segment. The matcher assigns segments to parameters in an intuitive way. For example:

get '*a/foo/*b', to: 'test#index'

would match zoo/woo/foo/bar/baz with params[:a] equals 'zoo/woo', and params[:b] equals 'bar/baz'.

get '*pages', to: 'pages#show', format: false

get '*pages', to: 'pages#show', format: true

3.12 Redirection

You can redirect any path to another path using the redirect helper in your router:

get '/stories', to: redirect('/articles')

You can also reuse dynamic segments from the match in the path to redirect to:

get '/stories/:name', to: redirect('/articles/%{name}')

You can also provide a block to redirect, which receives the symbolized path parameters and the request object:

get '/stories/:name', to: redirect { |path_params, req| "/articles/#{path_params[:name].pluralize}" }
get '/stories', to: redirect { |path_params, req| "/articles/#{req.subdomain}" }

Please note that this redirection is a 301 "Moved Permanently" redirect. Keep in mind that some web browsers or proxy servers will cache this type of redirect, making the old page inaccessible.

In all of these cases, if you don't provide the leading host (http://www.example.com), Rails will take those details from the current request.

3.13 Routing to Rack Applications

Instead of a String like 'articles#index', which corresponds to the index action in the ArticlesController, you can specify any Rack application as the endpoint for a matcher:

match '/application.js', to: Sprockets, via: :all

As long as Sprockets responds to call and returns a [status, headers, body], the router won't know the difference between the Rack application and an action. This is an appropriate use of via: :all, as you will want to allow your Rack application to handle all verbs as it considers appropriate.

If you specify a rack application as the endpoint for a matcher remember that the route will be unchanged in the receiving application. With the following route your rack application should expect the route to be '/admin':

match '/admin', to: AdminApp, via: :all

If you would prefer to have your rack application receive requests at the root path instead use mount:

mount AdminApp, at: '/admin'

3.14 Using root

You can specify what Rails should route '/' to with the root method:

root to: 'pages#main'
root 'pages#main' # shortcut for the above

You should put the root route at the top of the file, because it is the most popular route and should be matched first.

You can also use root inside namespaces and scopes as well. For example:

namespace :admin do
  root to: "admin#index"
end

root to: "home#index"

3.15 Unicode character routes

You can specify unicode character routes directly. For example:

get 'こんにちは', to: 'welcome#index'

4 Customizing Resourceful Routes

While the default routes and helpers generated by resources :articles will usually serve you well, you may want to customize them in some way. Rails allows you to customize virtually any generic part of the resourceful helpers.

4.1 Specifying a Controller to Use

The :controller option lets you explicitly specify a controller to use for the resource. For example:

resources :photos, controller: 'images'

will recognize incoming paths beginning with /photos but route to the Images controller:

HTTP Verb	Path	Controller#Action	Named Helper
GET	/photos	images#index	photos_path
GET	/photos/new	images#new	new_photo_path
POST	/photos	images#create	photos_path
GET	/photos/:id	images#show	photo_path(:id)
GET	/photos/:id/edit	images#edit	edit_photo_path(:id)
PATCH/PUT	/photos/:id	images#update	photo_path(:id)
DELETE	/photos/:id	images#destroy	photo_path(:id)

For namespaced controllers you can use the directory notation. For example:

resources :user_permissions, controller: 'admin/user_permissions'

This will route to the Admin::UserPermissions controller.

4.2 Specifying Constraints

You can use the :constraints option to specify a required format on the implicit id. For example:

resources :photos, constraints: { id: /[A-Z][A-Z][0-9]+/ }

This declaration constrains the :id parameter to match the supplied regular expression. So, in this case, the router would no longer match /photos/1 to this route. Instead, /photos/RR27 would match.

You can specify a single constraint to apply to a number of routes by using the block form:

constraints(id: /[A-Z][A-Z][0-9]+/) do
  resources :photos
  resources :accounts
end

4.3 Overriding the Named Helpers

The :as option lets you override the normal naming for the named route helpers. For example:

resources :photos, as: 'images'

will recognize incoming paths beginning with /photos and route the requests to PhotosController, but use the value of the :as option to name the helpers.

HTTP Verb	Path	Controller#Action	Named Helper
GET	/photos	photos#index	images_path
GET	/photos/new	photos#new	new_image_path
POST	/photos	photos#create	images_path
GET	/photos/:id	photos#show	image_path(:id)
GET	/photos/:id/edit	photos#edit	edit_image_path(:id)
PATCH/PUT	/photos/:id	photos#update	image_path(:id)
DELETE	/photos/:id	photos#destroy	image_path(:id)

4.4 Overriding the new and edit Segments

The :path_names option lets you override the automatically-generated new and edit segments in paths:

resources :photos, path_names: { new: 'make', edit: 'change' }

This would cause the routing to recognize paths such as:

/photos/make
/photos/1/change

scope path_names: { new: 'make' } do
  # rest of your routes
end

4.5 Prefixing the Named Route Helpers

You can use the :as option to prefix the named route helpers that Rails generates for a route. Use this option to prevent name collisions between routes using a path scope. For example:

scope 'admin' do
  resources :photos, as: 'admin_photos'
end

resources :photos

This will provide route helpers such as admin_photos_path, new_admin_photo_path, etc.

To prefix a group of route helpers, use :as with scope:

scope 'admin', as: 'admin' do
  resources :photos, :accounts
end

resources :photos, :accounts

This will generate routes such as admin_photos_path and admin_accounts_path which map to /admin/photos and /admin/accounts respectively.

You can prefix routes with a named parameter also:

scope ':username' do
  resources :articles
end

This will provide you with URLs such as /bob/articles/1 and will allow you to reference the username part of the path as params[:username] in controllers, helpers and views.

4.6 Restricting the Routes Created

By default, Rails creates routes for the seven default actions (index, show, new, create, edit, update, and destroy) for every RESTful route in your application. You can use the :only and :except options to fine-tune this behavior. The :only option tells Rails to create only the specified routes:

resources :photos, only: [:index, :show]

Now, a GET request to /photos would succeed, but a POST request to /photos (which would ordinarily be routed to the create action) will fail.

The :except option specifies a route or list of routes that Rails should not create:

resources :photos, except: :destroy

In this case, Rails will create all of the normal routes except the route for destroy (a DELETE request to /photos/:id).

4.7 Translated Paths

Using scope, we can alter path names generated by resources:

scope(path_names: { new: 'neu', edit: 'bearbeiten' }) do
  resources :categories, path: 'kategorien'
end

Rails now creates routes to the CategoriesController.

HTTP Verb	Path	Controller#Action	Named Helper
GET	/kategorien	categories#index	categories_path
GET	/kategorien/neu	categories#new	new_category_path
POST	/kategorien	categories#create	categories_path
GET	/kategorien/:id	categories#show	category_path(:id)
GET	/kategorien/:id/bearbeiten	categories#edit	edit_category_path(:id)
PATCH/PUT	/kategorien/:id	categories#update	category_path(:id)
DELETE	/kategorien/:id	categories#destroy	category_path(:id)

4.8 Overriding the Singular Form

If you want to define the singular form of a resource, you should add additional rules to the Inflector:

ActiveSupport::Inflector.inflections do |inflect|
  inflect.irregular 'tooth', 'teeth'
end

4.9 Using :as in Nested Resources

The :as option overrides the automatically-generated name for the resource in nested route helpers. For example:

resources :magazines do
  resources :ads, as: 'periodical_ads'
end

This will create routing helpers such as magazine_periodical_ads_url and edit_magazine_periodical_ad_path.

4.10 Overriding Named Route Parameters

The :param option overrides the default resource identifier :id (name of the dynamic segment used to generate the routes). You can access that segment from your controller using params[<:param>].

resources :videos, param: :identifier

videos GET  /videos(.:format)                  videos#index
            POST /videos(.:format)                  videos#create
 new_videos GET  /videos/new(.:format)              videos#new
edit_videos GET  /videos/:identifier/edit(.:format) videos#edit

Video.find_by(identifier: params[:identifier])

5 Inspecting and Testing Routes

Rails offers facilities for inspecting and testing your routes.

5.1 Listing Existing Routes

To get a complete list of the available routes in your application, visit http://localhost:3000/rails/info/routes in your browser while your server is running in the development environment. You can also execute the rake routes command in your terminal to produce the same output.

Both methods will list all of your routes, in the same order that they appear in routes.rb. For each route, you'll see:

• The route name (if any)
• The HTTP verb used (if the route doesn't respond to all verbs)
• The URL pattern to match
• The routing parameters for the route

For example, here's a small section of the rake routes output for a RESTful route:

users GET    /users(.:format)          users#index
          POST   /users(.:format)          users#create
 new_user GET    /users/new(.:format)      users#new
edit_user GET    /users/:id/edit(.:format) users#edit

You may restrict the listing to the routes that map to a particular controller setting the CONTROLLER environment variable:

$ CONTROLLER=users bin/rake routes

5.2 Testing Routes

Routes should be included in your testing strategy (just like the rest of your application). Rails offers three built-in assertions designed to make testing routes simpler:

• assert_generates
• assert_recognizes
• assert_routing

5.2.1 The assert_generates Assertion

assert_generates asserts that a particular set of options generate a particular path and can be used with default routes or custom routes. For example:

assert_generates '/photos/1', { controller: 'photos', action: 'show', id: '1' }
assert_generates '/about', controller: 'pages', action: 'about'

5.2.2 The assert_recognizes Assertion

assert_recognizes is the inverse of assert_generates. It asserts that a given path is recognized and routes it to a particular spot in your application. For example:

assert_recognizes({ controller: 'photos', action: 'show', id: '1' }, '/photos/1')

You can supply a :method argument to specify the HTTP verb:

assert_recognizes({ controller: 'photos', action: 'create' }, { path: 'photos', method: :post })

5.2.3 The assert_routing Assertion

The assert_routing assertion checks the route both ways: it tests that the path generates the options, and that the options generate the path. Thus, it combines the functions of assert_generates and assert_recognizes:

assert_routing({ path: 'photos', method: :post }, { controller: 'photos', action: 'create' })

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