Guides.rubyonrails.org

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
   • Paths and URLs
   • Defining Multiple Resources at the Same Time
   • Singular Resources
   • Controller Namespaces and Routing
   • Nested Resources
   • 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
   • Redirection
   • Routing to Rack Applications
   • Using root
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
5. Inspecting and Testing Routes
   • Seeing Existing Routes with rake
   • 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

GET /patients/17

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

match "/patients/:id" => "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 your application contains this code:

@patient = Patient.find(17)

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

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, 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:

2.3 Paths and URLs

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.

match "profile" => "users#show"

This resourceful route

resource :geocoder

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

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.

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 :posts, :comments
end

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

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

scope :module => "admin" do
  resources :posts, :comments
end

or, for a single case

resources :posts, :module => "admin"

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

scope "/admin" do
  resources :posts, :comments
end

or, for a single case

resources :posts, :path => "/admin/posts"

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 PostsController:

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:

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:

2.8 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, you could leave out the Array:

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

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

2.9 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.

2.9.1 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. 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 that it will recognize. You can use get, 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

2.9.2 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

2.9.3 A Note of Caution

If you find yourself adding many extra actions to a resourceful route, it’s time to stop and ask yourself whether you’re disguising the presence of another resource.

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 one of the default Rails routes:

match ':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:

match ':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".

match ':controller(/:action(/:id))', :controller => /admin\/[^\/]+/

3.3 Static Segments

You can specify static segments when creating a route:

match ':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:

match ':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:

match 'photos/:id' => '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:

match 'photos/:id' => '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.

match 'exit' => 'sessions#destroy', :as => :logout

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

3.7 HTTP Verb Constraints

You can use the :via option to constrain the request to one or more HTTP methods:

match 'photos/show' => 'photos#show', :via => :get

There is a shorthand version of this as well:

get 'photos/show'

You can also permit more than one verb to a single route:

match 'photos/show' => 'photos#show', :via => [:get, :post]

3.8 Segment Constraints

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

match 'photos/:id' => 'photos#show', :constraints => { :id => /[A-Z]\d{5}/ }

This route would match paths such as /photos/A12345. You can more succinctly express the same route this way:

match 'photos/:id' => '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:

match '/:id' => 'posts#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 posts 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:

match '/:id' => 'posts#show', :constraints => { :id => /\d.+/ }
match '/:username' => '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:

match "photos", :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

TwitterClone::Application.routes.draw do
  match "*path" => "blacklist#index",
    :constraints => BlacklistConstraint.new
end

3.11 Route Globbing

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

match 'photos/*other' => 'photos#unknown'

This route would match photos/12 or /photos/long/path/to/12, setting params[:other] to "12" or "long/path/to/12".

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

match 'books/*section/:title' => '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,

match '*a/foo/*b' => 'test#index'

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

match '*pages' => 'pages#show'

match '*pages' => 'pages#show', :format => false

match '*pages' => 'pages#show', :format => true

3.12 Redirection

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

match "/stories" => redirect("/posts")

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

match "/stories/:name" => redirect("/posts/%{name}")

You can also provide a block to redirect, which receives the params and (optionally) the request object:

match "/stories/:name" => redirect {|params| "/posts/#{params[:name].pluralize}" }
match "/stories" => redirect {|p, req| "/posts/#{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 "posts#index", which corresponds to the index action in the PostsController, you can specify any Rack application as the endpoint for a matcher.

match "/application.js" => Sprockets

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.

3.14 Using root

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

root :to => 'pages#main'

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 also need to delete the public/index.html file for the root route to take effect.

4 Customizing Resourceful Routes

While the default routes and helpers generated by resources :posts 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:

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.

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.

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 :posts
end

This will provide you with URLs such as /bob/posts/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.

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.

5 Inspecting and Testing Routes

Rails offers facilities for inspecting and testing your routes.

5.1 Seeing Existing Routes with rake

If you want a complete list of all of the available routes in your application, run rake routes command. This will print 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 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.

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.

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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