Action Dispatch Routing UrlFor

In config/routes.rb you define URL-to-controller mappings, but the reverse is also possible: a URL can be generated from one of your routing definitions. URL generation functionality is centralized in this module.

See ActionDispatch::Routing for general information about routing and config/routes.rb.

Tip: If you need to generate URLs from your models or some other place, then ActionDispatch::Routing::UrlFor is what you’re looking for. Read on for an introduction. In general, this module should not be included on its own, as it is usually included by url_helpers (as in Rails.application.routes.url_helpers).

URL generation from parameters

As you may know, some functions, such as ActionController::Base#url_for and ActionView::Helpers::UrlHelper#link_to, can generate URLs given a set of parameters. For example, you’ve probably had the chance to write code like this in one of your views:

<%= link_to('Click here', controller: 'users',
        action: 'new', message: 'Welcome!') %>
# => <a href="/users/new?message=Welcome%21">Click here</a>

link_to, and all other functions that require URL generation functionality, actually use ActionDispatch::Routing::UrlFor under the hood. And in particular, they use the ActionDispatch::Routing::UrlFor#url_for method. One can generate the same path as the above example by using the following code:

include ActionDispatch::Routing::UrlFor
url_for(controller: 'users',
        action: 'new',
        message: 'Welcome!',
        only_path: true)
# => "/users/new?message=Welcome%21"

Notice the only_path: true part. This is because UrlFor has no information about the website hostname that your Rails app is serving. So if you want to include the hostname as well, then you must also pass the :host argument:

include UrlFor
url_for(controller: 'users',
        action: 'new',
        message: 'Welcome!',
        host: 'www.example.com')
# => "http://www.example.com/users/new?message=Welcome%21"

By default, all controllers and views have access to a special version of url_for, that already knows what the current hostname is. So if you use url_for in your controllers or your views, then you don’t need to explicitly pass the :host argument.

For convenience, mailers also include ActionDispatch::Routing::UrlFor. So within mailers, you can use url_for. However, mailers cannot access incoming web requests in order to derive hostname information, so you have to provide the :host option or set the default host using default_url_options. For more information on url_for in mailers see the ActionMailer::Base documentation.

URL generation for named routes

UrlFor also allows one to access methods that have been auto-generated from named routes. For example, suppose that you have a ‘users’ resource in your config/routes.rb:

resources :users

This generates, among other things, the method users_path. By default, this method is accessible from your controllers, views, and mailers. If you need to access this auto-generated method from other places (such as a model), then you can do that by including Rails.application.routes.url_helpers in your class:

class User < ActiveRecord::Base
  include Rails.application.routes.url_helpers

  def base_uri
    user_path(self)
  end
end

User.find(1).base_uri # => "/users/1"

actionpack/lib/action_dispatch/routing/url_for.rb