Rails Routing from the Outside In

Chapters

1. The Purpose of the Rails Router
   • Routing Incoming URLs to Code
   • Generating Paths and URLs from Code
   • Configuring the Rails Router
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 Routes
3. Non-Resourceful Routes
   • Bound Parameters
   • Dynamic Segments
   • Static Segments
   • The Query String
   • Defining Default Parameters
   • Naming Routes
   • HTTP Verb Constraints
   • Segment Constraints
   • Request-Based Constraints
   • Advanced Constraints
   • Wildcard Segments
   • Format Segments
   • Redirection
   • Routing to Rack Applications
   • Using root
   • Unicode Character Routes
   • Direct Routes
   • Using resolve
4. Customizing Resourceful Routes
   • Specifying a Controller to Use
   • Specifying Constraints on id
   • Overriding the Named Route Helpers
   • Renaming the new and edit Path Names
   • Prefixing the Named Route Helpers with :as
   • Using :as in Nested Resources
   • Parametric Scopes
   • Restricting the Routes Created
   • Translated Paths
   • Specifying the Singular Form of a Resource
   • Renaming Default Route Parameter id
5. Inspecting Routes
   • Listing Existing Routes
   • Searching Routes
   • Listing Unused Routes
   • Routes in Rails Console
6. Testing Routes
   • The assert_generates Assertion
   • The assert_recognizes Assertion
   • The assert_routing Assertion
7. Breaking Up a Large Route File With draw

1 The Purpose of the Rails Router

The Rails router matches incoming HTTP requests to specific controller actions in your Rails application based on the URL path. (It can also forward to a Rack application.) The router also generates path and URL helpers based on the resources configured in the router.

1.1 Routing Incoming URLs to Code

When your Rails application receives an incoming request, it asks the router to match it to a controller action (aka method). For example, take the following incoming request:

GET /users/17

If the first matching route is:

get '/users/:id', to: 'user#show'

The request is matched to the UsersController class's show action with { id: '17' } in the params hash.

The to: option expects a controller#action format when passed a string. Alternatively, You can pass a symbol and use the action: option, instead of to:. You can also pass a string without a #, in which case the controller: option is used instead to to:. For example:

get '/users/:id', controller: 'users', action: :show

1.2 Generating Paths and URLs from Code

The Router automatically generates path and URL helper methods for your application. With these methods you can avoid hard-coded path and URL strings.

For example, the user_path and user_url helper methods are available when defining the following route:

get '/users/:id', to: 'users#show', as: 'user'

Assuming your application contains this code in the controller:

@user = User.find(params[:id])

and this in the corresponding view:

<%= link_to 'User Record', user_path(@user) %>

The router will generate the path /users/17 from user_path(@user). Using the user_path helper allows you to avoid having to hard-code a path in your views. This is helpful if you eventually move the route to a different URL, as you won't need to update the corresponding views.

It also generates user_url, which has a similar purpose. While user_path generates a relative URL like /users/17, user_url generates an absolute URL such as https://example.com/users/17 in the above example.

1.3 Configuring the Rails Router

Routes live in config/routes.rb. Here is an example of what routes look like in a typical Rails application. The sections that follow will explain the different route helpers used in this file:

Rails.application.routes.draw do
  resources :brands, only: [:index, :show] do
    resources :products, only: [:index, :show]
  end

  resource :basket, only: [:show, :update, :destroy]

  resolve("Basket") { route_for(:basket) }
end

Since this is a regular Ruby source file, you can use all of Ruby's features (like conditionals and loops) to help you define your routes.

2 Resource Routing: the Rails Default

Resource routing allows you to quickly declare all of the common routes for a given resource controller. For example, a single call to resources declares all of the necessary routes for the index, show, new, edit, create, update, and destroy actions, without you having to declare each route separately.

2.1 Resources on the Web

Browsers request pages from Rails by making a request for a URL using a specific HTTP verb, such as GET, POST, PATCH, PUT, and DELETE. Each HTTP verb is a request to perform an operation on the resource. A resource route maps 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 action on the PhotosController with { id: '17' } in params.

2.2 CRUD, Verbs, and Actions

In Rails, resourceful routes provide a mapping from incoming requests (a combination of HTTP verb + URL) to controller actions. By convention, each action generally maps to a specific CRUD operation on your data. A single entry in the routing file, such as:

resources :photos

creates seven different routes in your application, all mapping to the PhotosController actions:

Since the router uses the HTTP verb and path to match inbound requests, four URLs can map to seven different controller actions. For example, the same photos/ path matches to photos#index when the verb is GET and photos#create when the verb is POST.

2.3 Path and URL Helpers

Creating a resourceful route will also expose a number of helpers to controllers and views in your application.

For example, adding resources :photos to the route file will generate these _path helpers:

Parameters to the path helpers, such as :id above, are passed to the generated URL, such that edit_photo_path(10) will return /photos/10/edit.

Each of these _path helpers also have 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

The above is a shortcut for:

resources :photos
resources :books
resources :videos

2.5 Singular Resources

Sometimes, you have a resource that users expect to have only one (i.e. it does not make sense to have an index action to list all values of that resource). In that case, you can use resource (singular) instead of resources.

The below resourceful route creates six routes in your application, all mapping to the Geocoders controller:

resource :geocoder
resolve('Geocoder') { [:geocoder] }

Here are all of the routes created for a singular 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.

2.6 Controller Namespaces and Routing

In large applications, you may wish to organize groups of controllers under a namespace. For example, you may have a number of controllers under an Admin:: namespace, which are inside the app/controllers/admin directory. You can route to such a group by using a namespace block:

namespace :admin do
  resources :articles
end

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

Note that in the above example all of the paths have a /admin prefix per the default convention for namespace.

2.6.1 Using Module

If you want to route /articles (without the prefix /admin) to Admin::ArticlesController, you can specify the module with a scope block:

scope module: 'admin' do
  resources :articles
end

Another way to write the above:

resources :articles, module: 'admin'

2.6.2 Using Scope

Alternatively, you can also route /admin/articles to ArticlesController (without the Admin:: module prefix). You can specify the path with a scope block:

scope '/admin' do
  resources :articles
end

Another way to write the above:

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

For these alternatives (without /admin in path and without Admin:: in module prefix), the named route helpers remain the same as if you did not use scope.

In the last case, the following paths map to ArticlesController:

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 < ApplicationRecord
  has_many :ads
end

class Ad < ApplicationRecord
  belongs_to :magazine
end

Nested route declarations allow you to capture this relationship in your routing:

resources :magazines do
  resources :ads
end

In addition to the routes for magazines, this declaration will also route ads to an AdsController. Here are all of the routes for the nested ads resource:

This will also create the usual path and url routing helpers such as magazine_ads_url and edit_magazine_ad_path. Since the ads resource is nested below magazines, The ad URLs require a magazine. The helpers can take an instance of Magazine as the first parameter (edit_magazine_ad_path(@magazine, @ad)).

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

In the above 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. As you can see, deeply nested resources can become overly complex and cumbersome to maintain.

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.

For example:

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

Above we use the :only option which tells Rails to create only the specified routes. This idea strikes a balance between descriptive routes and deep nesting. There is a 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
end

The articles resource above will generate the following routes:

The shallow method with a block 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
  end
end

There are two options that can be used with scope to customize shallow routes - :shallow_path and :shallow_prefix.

The shallow_path option prefixes member paths with the given 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:

The :shallow_prefix option adds the specified parameter to the _path and _url route 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:

2.8 Routing Concerns

Routing concerns allow you to declare common routes that can be reused inside other resources. To define a concern, use a concern block:

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

You can also call concerns in a scope or namespace block to get the same result as above. For example:

namespace :messages do
  concerns :commentable
end

namespace :articles do
  concerns :commentable
  concerns :image_attachable
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) %>

The generated path will be something like /magazines/5/ads/42.

You can also use url_for with an array of objects to get the above path, like this:

<%= 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. An even shorter way to write that link_to is to specify just the object instead 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 need to insert the action name as the first element of the array, for edit_magazine_ad_path:

<%= 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 Routes

You are not limited to the seven routes that RESTful routing creates by default. You can add additional routes that apply to the collection or individual members of the collection.

The below sections describe adding member routes and collection routes. The term member refers to routes acting on a single element, such as show, update, or destroy. The term collection refers to routes acting on multiple, or a collection of, elements, such as the index route.

2.10.1 Adding Member Routes

You can add a member block into the resource block like this:

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

An incoming GET request to /photos/1/preview will route to the preview action of PhotosController. The resource id value will be available in params[:id]. It will also create the preview_photo_url and preview_photo_path helpers.

Within the member block, each route definition specifies the HTTP verb (get in the above example with get 'preview'). In addition to get, you can use patch, put, post, or delete.

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 also 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]. Route helpers will also be renamed from preview_photo_url and preview_photo_path to photo_preview_url and photo_preview_path.

2.10.2 Adding Collection Routes

To add a route to the collection, use a collection block:

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.

It is possible to customize the default routes and helpers generated by resources, see customizing resourceful routes section for more.

3 Non-Resourceful Routes

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

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

One example use case for non-resourceful routing is mapping existing 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. For example, consider this route:

get 'photos(/:id)', to: 'photos#display'

If an incoming GET request of /photos/1 is processed by this route, then the result will be to invoke the display 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#display, since :id is an optional parameter, denoted by parentheses in the above example.

3.2 Dynamic Segments

You can set up as many dynamic segments within a regular route as you like. Any segment will be available to the action as part of params. If you set up this route:

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

This route will respond to paths such as /photos/1/2. The params hash will be { controller: 'photos', action: 'show', id: '1', user_id: '2' }.

3.3 Static Segments

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

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

This route would respond to paths such as /photos/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 'photos/:id', to: 'photos#show'

An incoming GET request for /photos/1?user_id=2 will be dispatched to the show action of the PhotosController class as usual and the params hash will be { controller: 'photos', action: 'show', id: '1', user_id: '2' }.

3.5 Defining Default Parameters

You can define 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".

You can also use a defaults block to define the defaults for multiple items:

defaults format: :json do
  resources :photos
  resources :articles
end

3.6 Naming Routes

You can specify a name that will used by the _path and _url helpers for any route using the :as option:

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

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

You can also use as to override routing helper names defined by resources by placing a custom route definition before the resource is defined, like this:

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

This will define a user_path helper that will match /:username (e.g. /jane). Inside the show action of UsersController, params[:username] will contain the username for the user.

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. There is a match method that you could use with the :via option to match multiple verbs at once:

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

The above route matches GET and POST requests to the show action of the PhotosController.

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}/ }

The above route definition requires id to be 5 alphanumeric characters long. Therefore, 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}/

The :constraints option takes regular expressions (as well as any object that responds to matches? method) 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 and the end.

For example:

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

The above routes would allow sharing the root namespace and:

• route paths that always begin with a number, like /1-hello-world, to articles with id value.
• route paths that never begin with a number, like /david, to users with username value.

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. For example:

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

Will match an incoming request with a path to admin subdomain.

You can also specify constraints by using a constraints block:

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

Will match something like https://admin.example.com/photos.

Request constraints work by calling a method on the Request object with the same name as the hash key and then comparing the return value with the hash value. For example: constraints: { subdomain: 'api' } will match an api subdomain as expected. However, using a symbol constraints: { subdomain: :api } will not, because request.subdomain returns 'api' as a String.

There is an exception for the format constraint, while it's a method on the Request object, it's also an implicit optional parameter on every path. Segment constraints take precedence and the format constraint is only applied when enforced through a hash. For example, get 'foo', constraints: { format: 'json' } will match GET /foo because the format is optional by default.

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 restricted list to the RestrictedListController. You could do:

class RestrictedListConstraint
  def initialize
    @ips = RestrictedList.retrieve_ips
  end

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

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

You can also specify constraints as a lambda:

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

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

3.10.1 Constraints in a Block Form

You can specify constraints in a block form. This is useful for when you need to apply the same rule to several routes. For example:

class RestrictedListConstraint
  # ...Same as the example above
end

Rails.application.routes.draw do
  constraints(RestrictedListConstraint.new) do
    get '*path', to: 'restricted_list#index'
    get '*other-path', to: 'other_restricted_list#index'
  end
end

You can also use a lambda:

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

3.11 Wildcard Segments

A route definition can have a wildcard segment, which is a segment prefixed with a star, such as *other:

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

Wildcard segments allow for something called "route globbing", which is a way to specify that a particular parameter (*other above) be matched to the remaining part of a route.

So the above 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:

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 the order they occur. 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'.

3.12 Format Segments

Given this route definition:

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

By requesting '/foo/bar.json', your params[:pages] will be equal to 'foo/bar' with the request format of JSON in params[:format].

The default behavior with format is that if included Rails automatically captures it from the URL and includes it in params[:format], but format is not required in a URL.

If you want to match URLs without an explicit format and ignore URLs that include a format extension, you could supply format: false like this:

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

If you want to make the format segment mandatory, so it cannot be omitted, you can supply format: true like this:

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

3.13 Redirection

You can redirect any path to any other path by 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 default 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. You can use the :status option to change the response status:

get '/stories/:name', to: redirect('/articles/%{name}', status: 302)

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

3.14 Routing to Rack Applications

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

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

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

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'

3.15 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 typically put the root route at the top of the file so that it can be matched first.

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

root to: "home#index"

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

The above will match /admin to the index action for the AdminController and match / to index action of the HomeController.

3.16 Unicode Character Routes

You can specify unicode character routes directly. For example:

get 'こんにちは', to: 'welcome#index'

3.17 Direct Routes

You can create custom URL helpers by calling direct. For example:

direct :homepage do
  "https://rubyonrails.org"
end

# >> homepage_url
# => "https://rubyonrails.org"

The return value of the block must be a valid argument for the url_for method. So, you can pass a valid string URL, Hash, Array, an Active Model instance, or an Active Model class.

direct :commentable do |model|
  [ model, anchor: model.dom_id ]
end

direct :main do
  { controller: 'pages', action: 'index', subdomain: 'www' }
end

# >> main_url
# => "http://www.example.com/pages"

3.18 Using resolve

The resolve method allows customizing polymorphic mapping of models. For example:

resource :basket

resolve("Basket") { [:basket] }

<%= form_with model: @basket do |form| %>
  <!-- basket form -->
<% end %>

This will generate the singular URL /basket instead of the usual /baskets/:id.

4 Customizing Resourceful Routes

While the default routes and helpers generated by resources will usually serve you well, you may need to customize them in some way. Rails allows for several different ways to customize the resourceful routes and helpers. This section will detail the available options.

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:

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

resources :user_permissions, controller: 'admin/user_permissions'

This will route to the Admin::UserPermissionsController instance.

4.2 Specifying Constraints on id

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 given regular expression. 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 Route Helpers

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

resources :photos, as: 'images'

This will match /photos and route the requests to PhotosController as usual, but use the value of the :as option to name the helpers images_path etc., as shown:

4.4 Renaming the new and edit Path Names

The :path_names option lets you override the default new and edit segment in paths. For example:

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

This would allow paths such as /photos/make and /photos/1/change instead of /photos/new and /photos/1/edit.

It is also possible to change this option uniformly for all of your routes by using a scope block:

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

4.5 Prefixing the Named Route Helpers with :as

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 changes the route helpers for /admin/photos from photos_path, new_photos_path, etc. to admin_photos_path, new_admin_photo_path, etc. Without the addition of as: 'admin_photos' on the scoped resources :photos, the non-scoped resources :photos will not have any route helpers.

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

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

resources :photos, :accounts

Just as before, this changes the /admin scoped resource helpers to admin_photos_path and admin_accounts_path, and allows the non-scoped resources to use photos_path and accounts_path.

4.6 Using :as in Nested Resources

The :as option can override routing helper names for resources in nested routes as well. 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 instead of the default magazine_ads_url and edit_magazine_ad_path.

4.7 Parametric Scopes

You can prefix routes with a named parameter:

scope ':account_id', as: 'account', constraints: { account_id: /\d+/ } do
  resources :articles
end

This will provide you with paths such as /1/articles/9 and will allow you to reference the account_id part of the path as params[:account_id] in controllers, helpers, and views.

It will also generate path and URL helpers prefixed with account_, into which you can pass your objects as expected:

account_article_path(@account, @article) # => /1/article/9
url_for([@account, @article])            # => /1/article/9
form_with(model: [@account, @article])   # => <form action="/1/article/9" ...>

The :as option is also not mandatory, but without it, Rails will raise an error when evaluating url_for([@account, @article]) or other helpers that rely on url_for, such as form_with.

4.8 Restricting the Routes Created

By default, using resources creates routes for the seven default actions (index, show, new, create, edit, update, and destroy). You can use the :only and :except options to limit which routes are created.

The :only option tells Rails to create only the specified routes:

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

Now, a GET request to /photos or /photos/:id would succeed, but a POST request to /photos will fail to match.

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).

4.9 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.

4.10 Specifying the Singular Form of a Resource

If you need to override the singular form of a resource, you can add a rule to Active Support Inflector via inflections:

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

4.11 Renaming Default Route Parameter id

It is possible to rename the default parameter name id with the :param option. For example:

resources :videos, param: :identifier

Will now use params[:identifier] instead of params[:id].

    videos GET  /videos(.:format)                  videos#index
           POST /videos(.:format)                  videos#create
 new_video GET  /videos/new(.:format)              videos#new
edit_video GET  /videos/:identifier/edit(.:format) videos#edit

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

# Instead of
Video.find_by(id: params[:id])

You can override ActiveRecord::Base#to_param of the associated model to construct a URL:

class Video < ApplicationRecord
  def to_param
    identifier
  end
end

irb> video = Video.find_by(identifier: "Roman-Holiday")
irb> edit_video_path(video)
=> "/videos/Roman-Holiday/edit"

5 Inspecting Routes

Rails offers a few different ways of inspecting and testing your routes.

5.1 Listing Existing Routes

To get a complete list of routes available in an application, visit http://localhost:3000/rails/info/routes in the development environment. You can also execute the bin/rails routes command in your terminal to get the same output.

Both methods will list all of your routes, in the same order that they appear in config/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 bin/rails 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

The route name (new_user above, for example) can be considered the base for deriving route helpers. To get the name of a route helper, add the suffix _path or _url to the route name (new_user_path, for example).

You can also use the --expanded option to turn on the expanded table formatting mode.

$ bin/rails routes --expanded

--[ Route 1 ]----------------------------------------------------
Prefix            | users
Verb              | GET
URI               | /users(.:format)
Controller#Action | users#index
--[ Route 2 ]----------------------------------------------------
Prefix            |
Verb              | POST
URI               | /users(.:format)
Controller#Action | users#create
--[ Route 3 ]----------------------------------------------------
Prefix            | new_user
Verb              | GET
URI               | /users/new(.:format)
Controller#Action | users#new
--[ Route 4 ]----------------------------------------------------
Prefix            | edit_user
Verb              | GET
URI               | /users/:id/edit(.:format)
Controller#Action | users#edit

5.2 Searching Routes

You can search through your routes with the grep option: -g. This outputs any routes that partially match the URL helper method name, the HTTP verb, or the URL path.

$ bin/rails routes -g new_comment
$ bin/rails routes -g POST
$ bin/rails routes -g admin

If you only want to see the routes that map to a specific controller, there's the controller option: -c.

$ bin/rails routes -c users
$ bin/rails routes -c admin/users
$ bin/rails routes -c Comments
$ bin/rails routes -c Articles::CommentsController

5.3 Listing Unused Routes

You can scan your application for unused routes with the --unused option. An "unused" route in Rails is a route that is defined in the config/routes.rb file but is not referenced by any controller action or view in your application. For example:

$ bin/rails routes --unused
Found 8 unused routes:

     Prefix Verb   URI Pattern                Controller#Action
     people GET    /people(.:format)          people#index
            POST   /people(.:format)          people#create
 new_person GET    /people/new(.:format)      people#new
edit_person GET    /people/:id/edit(.:format) people#edit
     person GET    /people/:id(.:format)      people#show
            PATCH  /people/:id(.:format)      people#update
            PUT    /people/:id(.:format)      people#update
            DELETE /people/:id(.:format)      people#destroy

5.4 Routes in Rails Console

You can access route helpers using Rails.application.routes.url_helpers within the Rails Console. They are also available via the app object. For example:

irb> Rails.application.routes.url_helpers.users_path
=> "/users"

irb> user = User.first
=> #<User:0x00007fc1eab81628
irb> app.edit_user_path(user)
=> "/users/1/edit"

6 Testing Routes

Rails offers three built-in assertions designed to make testing routes simpler:

• assert_generates
• assert_recognizes
• assert_routing

6.1 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'

6.2 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 })

6.3 The assert_routing Assertion

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

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

7 Breaking Up a Large Route File With draw

In a large application with thousands of routes, a single config/routes.rb file can become cumbersome and hard to read. Rails offers a way to break up a single routes.rb file into multiple small ones using the draw macro.

For example, you could add an admin.rb file that contains all the routes related to the admin area, another api.rb file for API related resources, etc.

# config/routes.rb

Rails.application.routes.draw do
  get 'foo', to: 'foo#bar'

  draw(:admin) # Will load another route file located in `config/routes/admin.rb`
end

# config/routes/admin.rb

namespace :admin do
  resources :comments
end

Calling draw(:admin) inside the Rails.application.routes.draw block itself will try to load a route file that has the same name as the argument given (admin.rb in this example). The file needs to be located inside the config/routes directory or any sub-directory (i.e. config/routes/admin.rb or config/routes/external/admin.rb).

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