Rails Routing from the Outside In

1 The Purpose of the Rails Router

The Rails router recognizes URLs and dispatches them to a controller's action, or to a Rack application. 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(params[:id])

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.

1.3 Configuring the Rails Router

The routes for your application or engine live in the file config/routes.rb and typically looks like this:

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 its features to help you define your routes but be careful with variable names as they can clash with the DSL methods of the router.

2 Resource Routing: the Rails Default

Resource routing allows you to quickly declare all of the common routes for a given resource controller. A single call to resources can declare all of the necessary routes for your index, show, new, edit, create, update, and destroy actions.

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 action 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 a specific CRUD operation 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 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 to: will expect a controller#action format. When using a Symbol, the to: option should be replaced with action:. When using a String without a #, the to: option should be replaced with controller::

get 'profile', action: :show, controller: 'users'

This resourceful route:

resource :geocoder
resolve('Geocoder') { [: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, and place these controllers under the app/controllers/admin directory. You can route to such a group by using a namespace block:

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:

If instead 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, :comments
end

This can also be done for a single route:

resources :articles, module: 'admin'

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

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

This can also be done for a single route:

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

In both of these cases, 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 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:

2.7.2 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 articles resource here will have the following routes generated for it:

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:

The :shallow_prefix option adds the specified parameter to the named 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 and routes. 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 use them anywhere by calling concerns. For example, in a scope or namespace block:

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 that 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]. 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.

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 separately within your application.

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. For example, consider this route:

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

If an incoming request of /photos/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 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.

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'

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

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 route helpers in your application. Calling logout_path will return /exit

You can also use this to override routing methods defined by resources by placing custom routes before the resource is defined, like this:

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

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 and the end.

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 by using a constraints block:

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 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 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 segments 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 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 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: 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 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'

3.16 Direct Routes

You can create custom URL helpers directly 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

3.17 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 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:

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 Route 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. 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.

4.5.1 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" ...>

We are using a constraint to limit the scope to only match ID-like strings. You can change the constraint to suit your needs, or omit it entirely. The :as option is also not strictly required, 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.

4.6 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 override the singular form of a resource, you should add additional rules to the inflector via inflections:

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_video GET  /videos/new(.:format)              videos#new
edit_video GET  /videos/:identifier/edit(.:format) videos#edit

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

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

class Video < ApplicationRecord
  def to_param
    identifier
  end
end

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

5 Breaking Up Very Large Route File into Multiple Small Ones

If you work 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 a gigantic single routes.rb file into multiple small ones using the draw macro.

You could have an admin.rb route that contains all the routes for 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).

You can use the normal routing DSL inside the admin.rb routing file, but you shouldn't surround it with the Rails.application.routes.draw block like you did in the main config/routes.rb file.

5.1 Don't Use This Feature Unless You Really Need It

Having multiple routing files makes discoverability and understandability harder. For most applications - even those with a few hundred routes - it's easier for developers to have a single routing file. The Rails routing DSL already offers a way to break routes in an organized manner with namespace and scope.

6 Inspecting and Testing Routes

Rails offers facilities for inspecting and testing your routes.

6.1 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 bin/rails 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 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

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

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 -c option.

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

6.2 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

6.2.1 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'

6.2.2 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 })

6.2.3 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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