In routes.rb one defines URL-to-controller mappings, but the reverse
is also possible: an URL can be generated from one of your routing
definitions. URL generation functionality is centralized in this module.
See ActionController::Routing and ActionController::Resources for general
information about routing and routes.rb.
Tip: If you need to generate URLs from your models or some other
place, then ActionController::UrlWriter is
what you‘re looking for. Read on for an introduction.
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!') %>
#=> Generates a link to: /users/new?message=Welcome%21
link_to, and all other functions that require URL generation functionality,
actually use ActionController::UrlWriter under
the hood. And in particular, they use the ActionController::UrlWriter#url_for
method. One can generate the same path as the above example by using the
following code:
include UrlWriter
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 UrlWriter 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 UrlWriter
url_for(:controller => 'users',
:action => 'new',
:message => 'Welcome!',
:host => 'www.example.com') # Changed this.
# => "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 reasons, mailers provide a shortcut for ActionController::UrlWriter#url_for. So
within mailers, you only have to type ‘url_for’ instead of ‘ActionController::UrlWriter#url_for’
in full. However, mailers don‘t have hostname information, and
what‘s why you‘ll still have to specify the :host
argument when generating URLs in mailers.
URL generation for named routes
UrlWriter 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 routes.rb:
map.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 in two ways.
The first way is to include ActionController::UrlWriter in your class:
class User < ActiveRecord::Base
include ActionController::UrlWriter # !!!
def name=(value)
write_attribute('name', value)
write_attribute('base_uri', users_path) # !!!
end
end
The second way is to access them through ActionController::UrlWriter. The autogenerated
named routes methods are available as class methods:
class User < ActiveRecord::Base
def name=(value)
write_attribute('name', value)
path = ActionController::UrlWriter.users_path # !!!
write_attribute('base_uri', path) # !!!
end
end