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Rails Routing from the Outside In
=================================

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

After reading this guide, you will know:

* How to interpret the code in `config/routes.rb`.
* How to construct your own routes, using either the preferred resourceful style or the `match` method.
* How to declare route parameters, which are passed onto controller actions.
* How to automatically create paths and URLs using route helpers.
* Advanced techniques such as creating constraints and mounting Rack endpoints.

--------------------------------------------------------------------------------

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](rails_on_rack.html) application.) The router also generates path and URL
helpers based on the resources configured in the router.

### 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:

```ruby
get "/users/:id", to: "users#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 of `to:`. For example:

```ruby
get "/users/:id", controller: "users", action: :show
```

NOTE: Rails uses snake_case for controller names when specifying routes. For example, if you have a controller named `UserProfilesController`, you would specify a route to the show action as `user_profiles#show`.

### 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:

```ruby
get "/users/:id", to: "users#show", as: "user"
```

NOTE: The `as:` option is used to provide a custom name for a route, which is used when generating URL and path helpers.

Assuming your application contains this code in the controller:

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

and this in the corresponding view:

```erb
<%= 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.

### 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:

```ruby
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.

NOTE: The `Rails.application.routes.draw do ... end` block that wraps your route definitions is required to establish the scope for the router DSL (Domain Specific Language) and must not be deleted.

WARNING: Be careful with variable names in `routes.rb` as they can clash with the DSL methods of the router.

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.

[`resources`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html#method-i-resources

### 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:

```ruby
resources :photos
```

Rails would dispatch that request to the `destroy` action on the `PhotosController` with `{ id: '17' }` in `params`.

### 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](active_record_basics.html#crud-reading-and-writing-data) operation on your data. A single entry in
the routing file, such as:

```ruby
resources :photos
```

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

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

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`.

NOTE: Order matters in the `routes.rb` file. Rails routes are matched in the order they are specified. For example, if you have a `resources :photos` above a `get 'photos/poll'` the `show` action's route for the `resources` line will be matched before the `get` line. If you want the `photos/poll` route to match first, you'll need to move the `get` line **above** the `resources` line.

### 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:

| Path Helper | Returns URL |
| --------- | ---------------- |
| `photos_path` | /photos |
| `new_photo_path` | /photos/new |
| `edit_photo_path(:id)` | /photos/:id/edit |
| `photo_path(:id)` | /photos/:id |

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.

TIP: The prefix used before "_path" and "_url" is the route name and can be identified by looking at the "prefix" column of the `bin/rails routes` command output. To learn more see [Listing Existing Routes](#listing-existing-routes) below.

### 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`:

```ruby
resources :photos, :books, :videos
```

The above is a shortcut for:

```ruby
resources :photos
resources :books
resources :videos
```

### 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:

```ruby
resource :geocoder
resolve("Geocoder") { [:geocoder] }
```

NOTE: The call to `resolve` is necessary for converting instances of the `Geocoder` to singular routes through [record identification](form_helpers.html#relying-on-record-identification).

Here are all of the routes created for a singular resource:

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

NOTE: Singular resources map to plural controllers. For example, the `geocoder` resource maps to the `GeocodersController`.

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.

### 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:

```ruby
namespace :admin do
  resources :articles
end
```

For `Admin::ArticlesController`, Rails will create the following routes:

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

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

#### Using Module

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

```ruby
scope module: "admin" do
  resources :articles
end
```

Another way to write the above:

```ruby
resources :articles, module: "admin"
```

#### 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:

```ruby
scope "/admin" do
  resources :articles
end
```

Another way to write the above:

```ruby
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`:

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

TIP: If you need to use a different controller namespace inside a `namespace` block you can specify an absolute controller path, e.g: `get '/foo', to: '/foo#index'`.

[`namespace`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Scoping.html#method-i-namespace
[`scope`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Scoping.html#method-i-scope

### Nested Resources

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

```ruby
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:

```ruby
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:

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

This will also create 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)`).

#### Limits to Nesting

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

```ruby
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.

TIP: The general rule of thumb is to only nest resources 1 level deep.

#### 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.

NOTE: The "member" actions are the ones that apply to an individual resource and require an ID to identify the specific resource they are acting upon, such as `show`, `edit`, etc. The "collection" actions are the ones that act on the entire set of the resource, such as `index`.

For example:

```ruby
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:

```ruby
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:

```ruby
resources :articles, shallow: true do
  resources :comments
  resources :quotes
end
```

The articles resource above will generate the following routes:

| HTTP Verb | Path                                         | Controller#Action | Named Route Helper       |
| --------- | -------------------------------------------- | ----------------- | ------------------------ |
| GET       | /articles/:article_id/comments(.:format)     | comments#index    | article_comments_path    |
| POST      | /articles/:article_id/comments(.:format)     | comments#create   | article_comments_path    |
| GET       | /articles/:article_id/comments/new(.:format) | comments#new      | new_article_comment_path |
| GET       | /comments/:id/edit(.:format)                 | comments#edit     | edit_comment_path        |
| GET       | /comments/:id(.:format)                      | comments#show     | comment_path             |
| PATCH/PUT | /comments/:id(.:format)                      | comments#update   | comment_path             |
| DELETE    | /comments/:id(.:format)                      | comments#destroy  | comment_path             |
| GET       | /articles/:article_id/quotes(.:format)       | quotes#index      | article_quotes_path      |
| POST      | /articles/:article_id/quotes(.:format)       | quotes#create     | article_quotes_path      |
| GET       | /articles/:article_id/quotes/new(.:format)   | quotes#new        | new_article_quote_path   |
| GET       | /quotes/:id/edit(.:format)                   | quotes#edit       | edit_quote_path          |
| GET       | /quotes/:id(.:format)                        | quotes#show       | quote_path               |
| PATCH/PUT | /quotes/:id(.:format)                        | quotes#update     | quote_path               |
| DELETE    | /quotes/:id(.:format)                        | quotes#destroy    | quote_path               |
| GET       | /articles(.:format)                          | articles#index    | articles_path            |
| POST      | /articles(.:format)                          | articles#create   | articles_path            |
| GET       | /articles/new(.:format)                      | articles#new      | new_article_path         |
| GET       | /articles/:id/edit(.:format)                 | articles#edit     | edit_article_path        |
| GET       | /articles/:id(.:format)                      | articles#show     | article_path             |
| PATCH/PUT | /articles/:id(.:format)                      | articles#update   | article_path             |
| DELETE    | /articles/:id(.:format)                      | articles#destroy  | article_path             |

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:

```ruby
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:

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

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

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

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

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

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

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

[`shallow`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html#method-i-shallow

### 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:

```ruby
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:

```ruby
resources :messages, concerns: :commentable

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

The above is equivalent to:

```ruby
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:

```ruby
namespace :messages do
  concerns :commentable
end

namespace :articles do
  concerns :commentable
  concerns :image_attachable
end
```

[`concern`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Concerns.html#method-i-concern
[`concerns`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Concerns.html#method-i-concerns

### 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:

```ruby
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:

```erb
<%= 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`][ActionView::RoutingUrlFor#url_for] with an array of objects to get the above path, like this:

```erb
<%= 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`](https://api.rubyonrails.org/classes/ActionView/Helpers/NavigationHelper.html#method-i-link_to) is to specify just the object instead of the full [`url_for`](https://api.rubyonrails.org/classes/ActionDispatch/Routing/UrlFor.html) call:

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

If you wanted to link to just a magazine:

```erb
<%= 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`:

```erb
<%= 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.

NOTE: In order to automatically derive paths and URLs from objects such as `[@magazine, @ad]`, Rails uses methods from [`ActiveModel::Naming`](https://api.rubyonrails.org/classes/ActiveModel/Naming.html) and [`ActiveModel::Conversion`](https://api.rubyonrails.org/classes/ActiveModel/Conversion.html) modules. Specifically, the `@magazine.model_name.route_key` returns `magazines` and `@magazine.to_param` returns a string representation of the model's `id`. So the generated path may be something like `/magazines/1/ads/42` for the objects `[@magazine, @ad]`.

[ActionView::RoutingUrlFor#url_for]: https://api.rubyonrails.org/classes/ActionView/RoutingUrlFor.html#method-i-url_for

### Adding More RESTful Routes

You are not limited to the [seven routes](#crud-verbs-and-actions) 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.

#### Adding Member Routes

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

```ruby
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:

```ruby
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`.

[`delete`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/HttpHelpers.html#method-i-delete
[`get`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/HttpHelpers.html#method-i-get
[`member`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html#method-i-member
[`patch`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/HttpHelpers.html#method-i-patch
[`post`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/HttpHelpers.html#method-i-post
[`put`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/HttpHelpers.html#method-i-put
[`put`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/HttpHelpers.html#method-i-put

#### Adding Collection Routes

To add a route to the collection, use a [`collection`][] block:

```ruby
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:

```ruby
resources :photos do
  get "search", on: :collection
end
```

NOTE: If you're defining additional resource routes with a symbol as the first positional argument, be mindful that it is not equivalent to using a string. Symbols infer controller actions while strings infer paths.

[`collection`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html#method-i-collection

#### Adding Routes for Additional New Actions

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

```ruby
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.

TIP: 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.

It is possible to customize the default routes and helpers generated by `resources`, see [customizing resourceful routes section](#customizing-resourceful-routes) for more.

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.

### 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:

```ruby
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.

### 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:

```ruby
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' }.

TIP: By default, dynamic segments don't accept dots - this is because the dot is used as a separator for formatted routes. If you need to use a dot within a dynamic segment, add a constraint that overrides this – for example, `id: /[^\/]+/` allows anything except a slash.

### Static Segments

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

```ruby
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' }`.

### The Query String

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

```ruby
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' }`.

### 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:

```ruby
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:

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

NOTE: You cannot override defaults via query parameters - this is for security reasons. The only defaults that can be overridden are dynamic segments via substitution in the URL path.

[`defaults`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Scoping.html#method-i-defaults

### Naming Routes

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

```ruby
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:

```ruby
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.

### 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:

```ruby
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`:

```ruby
match "photos", to: "photos#show", via: :all
```

NOTE: Routing both `GET` and `POST` requests to a single action has security
implications. For example, the `GET` action won't check for CSRF token (so
writing to the database from `GET` request is not a good idea. For more
information see the [security guide](security.html#csrf-countermeasures)). In
general, avoid routing all verbs to a single action unless you have a good
reason.

[`match`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Base.html#method-i-match

### Segment Constraints

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

```ruby
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:

```ruby
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:

```ruby
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:

```ruby
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.

### Request-Based Constraints

You can also constrain a route based on any method on the [Request object](action_controller_overview.html#the-request-object) that returns a `String`.

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

```ruby
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:

```ruby
constraints subdomain: "admin" do
  resources :photos
end
```

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

Request constraints work by calling a method on the [Request object](action_controller_overview.html#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.

NOTE: Constraint values should match the corresponding Request object method return type.

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.

NOTE: You can [use a lambda](#advanced-constraints) like in `get 'foo', constraints: lambda { |req| req.format == :json }` to only match the route to explicit JSON requests.

[`constraints`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Scoping.html#method-i-constraints

### 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:

```ruby
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:

```ruby
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 get the `request` object as an argument.

#### 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:

```ruby
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`:

```ruby
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
```

### Wildcard Segments

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

```ruby
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:

```ruby
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:

```ruby
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'`.

### Format Segments

Given this route definition:

```ruby
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:

```ruby
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:

```ruby
get "*pages", to: "pages#show", format: true
```

### Redirection

You can redirect any path to any other path by using the [`redirect`][] helper in your router:

```ruby
get "/stories", to: redirect("/articles")
```

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

```ruby
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:

```ruby
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:

```ruby
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.

[`redirect`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Redirection.html#method-i-redirect

### 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](rails_on_rack.html) as the endpoint for a matcher:

```ruby
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.

NOTE: An interesting tidbit - `'articles#index'` expands out to `ArticlesController.action(:index)`, which returns a valid Rack application.

NOTE: Since procs/lambdas are objects that respond to `call`, you can implement very simple routes (e.g. for health checks) inline, something like: `get '/health', to: ->(env) { [204, {}, ['']] }`

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`:

```ruby
match "/admin", to: AdminApp, via: :all
```

If you would prefer to have your Rack application receive requests at the root
path instead, use [`mount`][]:

```ruby
mount AdminApp, at: "/admin"
```

[`mount`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Base.html#method-i-mount

### Using `root`

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

```ruby
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.

NOTE: The `root` route primarily handles `GET` requests by default. But it is possible to configure it to handle other verbs (e.g. `root "posts#index", via: :post`)

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

```ruby
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`.

[`root`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html#method-i-root

### Unicode Character Routes

You can specify unicode character routes directly. For example:

```ruby
get "こんにちは", to: "welcome#index"
```

### Direct Routes

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

```ruby
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.

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

```ruby
direct :main do
  { controller: "pages", action: "index", subdomain: "www" }
end

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

[`direct`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/CustomUrls.html#method-i-direct
[`url_for`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/UrlFor.html

### Using `resolve`

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

```ruby
resource :basket

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

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

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

[`resolve`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/CustomUrls.html#method-i-resolve

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.

### Specifying a Controller to Use

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

```ruby
resources :photos, controller: "images"
```

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

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

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

```ruby
resources :user_permissions, controller: "admin/user_permissions"
```

This will route to the `Admin::UserPermissionsController` instance.

NOTE: Only the directory notation is supported. Specifying the controller with
Ruby constant notation (e.g. `controller: 'Admin::UserPermissions'`) is not supported.

### Specifying Constraints on `id`

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

```ruby
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:

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

NOTE: You can use the more [advanced constraints](#advanced-constraints) available in non-resourceful routes section in this context as well.

TIP: By default the `:id` parameter doesn't accept dots - this is because the dot is used as a separator for formatted routes. If you need to use a dot within an `:id` add a constraint which overrides this - for example `id: /[^\/]+/` allows anything except a slash.

### Overriding the Named Route Helpers

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

```ruby
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:

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

### Renaming the `new` and `edit` Path Names

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

```ruby
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`.

NOTE: The route helpers and controller action names aren't changed by this option. The two paths shown would have `new_photo_path` and `edit_photo_path` helpers and still route to the `new` and `edit` actions.

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

```ruby
scope path_names: { new: "make" } do
  # rest of your routes
end
```

### 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:

```ruby
scope "admin" do
  resources :photos, as: "admin_photos"
end

resources :photos
```

This changes the route helpers for `/admin/photos` from `photos_path`,
`new_photo_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`:

```ruby
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`.

NOTE: The `namespace` scope will automatically add `:as` as well as `:module` and `:path` prefixes.

### Using `:as` in Nested Resources

The `:as` option can override routing helper names for resources in nested routes as well. For example:

```ruby
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`.

### Parametric Scopes

You can prefix routes with a named parameter:

```ruby
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:

```ruby
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`][].

[`form_with`]: https://api.rubyonrails.org/classes/ActionView/Helpers/FormHelper.html#method-i-form_with

### 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:

```ruby
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:

```ruby
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`).

TIP: If your application has many RESTful routes, using `:only` and `:except` to
generate only the routes that you actually need can cut down on memory use and
speed up the routing process by eliminating [unused
routes](#listing-unused-routes).

### Translated Paths

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

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

Rails now creates routes to the `CategoriesController`.

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

### 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`][]:

```ruby
ActiveSupport::Inflector.inflections do |inflect|
  inflect.irregular "tooth", "teeth"
end
```

[`inflections`]: https://api.rubyonrails.org/classes/ActiveSupport/Inflector.html#method-i-inflections

### Renaming Default Route Parameter `id`

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

```ruby
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
```

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

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

You can override [`ActiveRecord::Base#to_param`](https://api.rubyonrails.org/classes/ActiveRecord/Integration.html#method-i-to_param) of the associated model to construct a URL:

```ruby
class Video < ApplicationRecord
  def to_param
    identifier
  end
end
```

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

Inspecting Routes
-----------------

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

### 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.

```bash
$ 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
```

### 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.

```bash
$ 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`.

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

TIP: The output from `bin/rails routes` is easier to read if you widen your terminal window until the output lines don't wrap or use the `--expanded` option.

### 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:

```bash
$ 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
```

### Routes in Rails Console

You can access route helpers using `Rails.application.routes.url_helpers` within the [Rails Console](command_line.html#bin-rails-console). They are also available via the [app](command_line.html#the-app-object) object. For example:

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

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

Testing Routes
--------------

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

* [`assert_generates`][]
* [`assert_recognizes`][]
* [`assert_routing`][]

[`assert_generates`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html#method-i-assert_generates
[`assert_recognizes`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html#method-i-assert_recognizes
[`assert_routing`]: https://api.rubyonrails.org/classes/ActionDispatch/Assertions/RoutingAssertions.html#method-i-assert_routing

### 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:

```ruby
assert_generates "/photos/1", { controller: "photos", action: "show", id: "1" }
assert_generates "/about", controller: "pages", action: "about"
```

### 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:

```ruby
assert_recognizes({ controller: "photos", action: "show", id: "1" }, "/photos/1")
```

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

```ruby
assert_recognizes({ controller: "photos", action: "create" }, { path: "photos", method: :post })
```

### 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:

```ruby
assert_routing({ path: "photos", method: :post }, { controller: "photos", action: "create" })
```

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.

```ruby
# 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
```

```ruby
# 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`).

NOTE: You can use the normal routing DSL inside a secondary routing file such as `admin.rb`, but *do not* surround it with the `Rails.application.routes.draw` block. That should be used in the main `config/routes.rb` file only.

[`draw`]: https://api.rubyonrails.org/classes/ActionDispatch/Routing/Mapper/Resources.html#method-i-draw

NOTE: Don't use this feature unless you really need it. Having multiple routing files makes it harder to discover routes in one place. 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`.
