Rails routing is a two-way piece of machinery - rather as if you could turn trees into paper, and then turn paper back into trees. Specifically, it both connects incoming HTTP requests to the code in your application's controllers, and helps you generate URLs without having to hard-code them as strings.
the routing engine within Rails is the piece of code that dispatches the request to the appropriate spot in your application. In this case, the application would most likely end up running the +show+ action within the +patients+ controller, displaying the details of the patient whose ID is 17.
Then the routing engine is the piece that translates that to a link to a URL such as +http://example.com/patients/17+. By using routing in this way, you can reduce the brittleness of your application as compared to one with hard-coded URLs, and make your code easier to read and understand.
NOTE: Patient needs to be declared as a resource for this style of translation via a named route to be available.
There are two components to routing in Rails: the routing engine itself, which is supplied as part of Rails, and the file +config/routes.rb+, which contains the actual routes that will be used by your application. Learning exactly what you can put in +routes.rb+ is the main topic of this guide, but before we dig in let's get a quick overview.
In format, +routes.rb+ is nothing more than one big block sent to +ActionController::Routing::Routes.draw+. Within this block, you can have comments, but it's likely that most of your content will be individual lines of code - each line being a route in your application. You'll find five main types of content in this file:
* RESTful Routes
* Named Routes
* Nested Routes
* Regular Routes
* Default Routes
Each of these types of route is covered in more detail later in this guide.
The +routes.rb+ file is processed from top to bottom when a request comes in. The request will be dispatched to the first matching route. If there is no matching route, then Rails returns HTTP status 404 to the caller.
RESTful routes take advantage of the built-in REST orientation of Rails to wrap up a lot of routing information in a single declaration. A RESTful route looks like this:
Nested routes let you declare that one resource is contained within another resource. You'll see later on how this translates to URLs and paths in your code. For example, if your application includes parts, each of which belongs to an assembly, you might have this nested route declaration:
These default routes are automatically generated when you create a new Rails application. If you're using RESTful routing for everything in your application, you will probably want to remove them. But be sure you're not using the default routes before you remove them!
RESTful routing is the current standard for routing in Rails, and it's the one that you should prefer for new applications. It can take a little while to understand how RESTful routing works, but it's worth the effort; your code will be easier to read and you'll be working with Rails, rather than fighting against it, when you use this style of routing.
The foundation of RESTful routing is generally considered to be Roy Fielding's doctoral thesis, "Architectural Styles and the Design of Network-based Software Architectures":http://www.ics.uci.edu/~fielding/pubs/dissertation/top.htm. Fortunately, you need not read this entire document to understand how REST works in Rails. REST, an acronym for Representational State Transfer, boils down to two main principles for our purposes:
would be understood to refer to a photo resource with the ID of 17, and to indicate a desired action - deleting that resource. REST is a natural style for the architecture of web applications, and Rails makes it even more natural by using conventions to shield you from some of the RESTful complexities.
In Rails, a RESTful route provides a mapping between HTTP verbs, controller actions, and (implicitly) CRUD operations in a database. A single entry in the routing file, such as
For the specific routes (those that reference just a single resource), the identifier for the resource will be available within the corresponding controller action as +params[:id]+.
TIP: If you consistently use RESTful routes in your application, you should disable the default routes in +routes.rb+ so that Rails will enforce the mapping between HTTP verbs and routes.
Creating a RESTful route will also make available a pile of helpers within your application:
* +photos_url+ and +photos_path+ map to the path for the index and create actions
* +new_photo_url+ and +new_photo_path+ map to the path for the new action
* +edit_photo_url+ and +edit_photo_path+ map to the path for the edit action
* +photo_url+ and +photo_path+ map to the path for the show, update, and destroy actions
NOTE: Because routing makes use of the HTTP verb as well as the path in the request to dispatch requests, the seven routes generated by a RESTful routing entry only give rise to four pairs of helpers.
In each case, the +_url+ helper generates a string containing the entire URL that the application will understand, while the +_path+ helper generates a string containing the relative path from the root of the application. For example:
If you need to create routes for more than one RESTful resource, you can save a bit of typing by defining them all with a single call to +map.resources+:
You can also apply RESTful routing to singleton resources within your application. In this case, you use +map.resource+ instead of +map.resources+ and the route generation is slightly different. For example, a routing entry of
Although the conventions of RESTful routing are likely to be sufficient for many applications, there are a number of ways to customize the way that RESTful routes work. These options include:
NOTE: The helpers will be generated with the name of the resource, not the name of the controller. So in this case, you'd still get +photos_path+, +new_photo_path+, and so on.
Rails allows you to group your controllers into namespaces by saving them in folders underneath +app/controllers+. The +:controller+ option provides a convenient way to use these routes. For example, you might have a resource whose controller is purely for admin users in the +admin+ folder:
If you use controller namespaces, you need to be aware of a subtlety in the Rails routing code: it always tries to preserve as much of the namespace from the previous request as possible. For example, if you are on a view generated from the +adminphoto_path+ helper, and you follow a link generated with +<%= link_to "show", adminphoto(1) %>+ you will end up on the view generated by +admin/photos/show+, but you will also end up in the same place if you have +<%= link_to "show", {:controller => "photos", :action => "show"} %>+ because Rails will generate the show URL relative to the current URL.
TIP: If you want to guarantee that a link goes to a top-level controller, use a preceding slash to anchor the controller name: +<%= link_to "show", {:controller => "/photos", :action => "show"} %>+
If for some reason Rails isn't doing what you want in converting the plural resource name to a singular name in member routes, you can override its judgment with the +:singular+ option:
This declaration constrains the +:id+ parameter to match the supplied regular expression. So, in this case, +/photos/1+ would no longer be recognized by this route, but +/photos/RR27+ would.
Conditions in Rails routing are currently used only to set the HTTP verb for individual routes. Although in theory you can set this for RESTful routes, in practice there is no good reason to do so. (You'll learn more about conditions in the discussion of classic routing later in this guide.)
NOTE: The helpers will be generated with the name of the resource, not the path name. So in this case, you'd still get +photos_path+, +new_photo_path+, and so on.
The +:path_prefix+ option lets you add additional parameters that will be prefixed to the recognized paths. For example, suppose each photo in your application belongs to a particular photographer. In that case, you might declare this route:
You can use the :name_prefix option to avoid collisions between routes. This is most useful when you have two resources with the same name that use +:path_prefix+ to map differently. For example:
By default, Rails creates routes for all seven of the 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 specifies that only certain routes should be generated:
With this declaration, 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 should _not_ be generated:
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.
Each ad is logically subservient to one magazine. Nested routes allow you to capture this relationship in your routing. In this case, you might include this route declaration:
In addition to the routes for magazines, this declaration will also create routes for ads, each of which requires the specification of a magazine in the URL:
This will create routing helpers such as +periodical_ads_url+ and +periodical_edit_ad_path+. You can even use +:name_prefix+ to suppress the prefix entirely:
The +:has_one+ and +:has_many+ options provide a succinct notation for simple nested routes. Use +:has_one+ to nest a singleton resource, or +:has_many+ to nest a plural resource:
However, without the use of +name_prefix => nil+, deeply-nested resources quickly become cumbersome. In this case, for example, the application would recognize URLs such as
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":http://weblog.jamisbuck.org/2007/2/5/nesting-resources by Jamis Buck proposes a rule of thumb for good Rails design:
The +:shallow+ option provides an elegant solution to the difficulties of deeply-nested routes. If you specify this option at any level of routing, then paths for nested resources which reference a specific member (that is, those with an +:id+ parameter) will not use the parent path prefix or name prefix. To see what this means, consider this set of routes:
With shallow nesting, you need only supply enough information to uniquely identify the resource that you want to work with. If you like, you can combine shallow nesting with the +:has_one+ and +:has_many+ options:
In addition to using the generated routing helpers, Rails can also generate RESTful routes from an array of parameters. For example, suppose you have a set of routes generated with these entries in routes.rb:
It's possible to do some quite complex things by combining +:path_prefix+ and +:name_prefix+. For example, you can use the combination of these two options to move administrative resources to their own folder in your application:
The good news is that if you find yourself using this level of complexity, you can stop. Rails supports _namespaced resources_ to make placing resources in their own folder a snap. Here's the namespaced version of those same three routes:
As you can see, the namespaced version is much more succinct than the one that spells everything out - but it still creates the same routes. For example, you'll get +admin_photos_url+ that expects to find an +Admin::PhotosController+ and that matches +admin/photos+, and +admin_photos_ratings_path+ that matches +/admin/photos/_photo_id_/ratings+, expecting to use +Admin::RatingsController+. Even though you're not specifying +path_prefix+ explicitly, the routing code will calculate the appropriate +path_prefix+ from the route nesting.
You are not limited to the seven routes that RESTful routing creates by default. If you like, you may add additional member routes (those which apply to a single instance of the resource), additional new routes (those that apply to creating a new resource), or additional collection routes (those which apply to the collection of resources as a whole).
This will enable Rails to recognize URLs such as +/photos/1/preview+ using the GET HTTP verb, and route them to the preview action of the Photos controller. It will also create a +preview_photo+ route helper.
Within the hash of member routes, each route name specifies the HTTP verb that it will recognize. You can use +:get+, +:put+, +:post+, +:delete+, or +:any+ here. You can also specify an array of methods, if you need more than one but you don't want to allow just anything:
This will enable Rails to recognize URLs such as +/photos/search+ using the GET HTTP verb, and route them to the search action of the Photos controller. It will also create a +search_photos+ route helper.
Just as with member routes, you can specify an array of methods for a collection route:
This will enable Rails to recognize URLs such as +/photos/upload+ using the POST HTTP verb, and route them to the upload action of the Photos controller. It will also create a +upload_photos+ route helper.
TIP: If you want to redefine the verbs accepted by one of the standard actions, you can do so by explicitly mapping that action. For example:<br/>+map.resources :photos, :new => { :new => :any }+<br/>This will allow the new action to be invoked by any request to +photos/new+, no matter what HTTP verb you use.
If you find yourself adding many extra actions to a RESTful route, it's time to stop and ask yourself whether you're disguising the presence of another resource that would be better split off on its own. When the +:member+ and +:collection+ hashes become a dumping-ground, RESTful routes lose the advantage of easy readability that is one of their strongest points.
In addition to RESTful routing, Rails supports regular routing - a way to map URLs to controllers and actions. With regular routing, you don't get the masses of routes automatically generated by RESTful routing. Instead, you must set up each route within your application separately.
While RESTful routing has become the Rails standard, there are still plenty of places where the simpler regular routing works fine. You can even mix the two styles within a single application. In general, you should prefer RESTful routing _when possible_, because it will make parts of your application easier to write. But there's no need to try to shoehorn every last piece of your application into a RESTful framework if that's not a good fit.
When you set up a regular route, you supply a series of symbols that Rails maps to parts of an incoming HTTP request. Two of these symbols are special: +:controller+ maps to the name of a controller in your application, and +:action+ maps to the name of an action within that controller. For example, consider one of the default Rails routes:
If an incoming request of +/photos/show/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 +show+ action of the +Photos+ controller, and to make the final parameter (1) available as +params[:id]+.
You can set up as many wildcard symbols within a regular route as you like. Anything other than +:controller+ or +:action+ will be available to the matching action as part of the params hash. So, if you set up this route:
An incoming URL of +/photos/show/1/2+ will be dispatched to the +show+ action of the +Photos+ controller. +params[:id]+ will be set to 1, and +params[:user_id]+ will be set to 2.
An incoming URL of +/photos/show/1?user_id=2+ will be dispatched to the +show+ action of the +Photos+ controller. +params[:id]+ will be set to 1, and +params[:user_id]+ will be equal to 2.
You can also define other defaults in a route by supplying a hash for the +:defaults+ option. This even applies to parameters that are not explicitly defined elsewhere in the route. For example:
With this route, an incoming URL of +photos/12+ would be dispatched to the +show+ action within the +Photos+ controller, and +params[:format]+ will be set to +jpg+.
This will do two things. First, requests to +/logout+ will be sent to the +destroy+ method of the +Sessions+ controller. Second, Rails will maintain the +logout_path+ and +logout_url+ helpers for use within your code.
Route conditions (introduced with the +:conditions+ option) are designed to implement restrictions on routes. Currently, the only supported restriction is +:method+:
There's one more way in which routing can do different things depending on differences in the incoming HTTP request: by issuing a response that corresponds to what the request specifies that it will accept. In Rails routing, you can control this with the special +:format+ parameter in the route.
For instance, consider the second of the default routes in the boilerplate +routes.rb+ file:
This route matches requests such as +/photo/edit/1.xml+ or +/photo/show/2.rss+. Within the appropriate action code, you can issue different responses depending on the requested format:
By default, Rails recognizes +html+, +text+, +json+, +csv+, +xml+, +rss+, +atom+, and +yaml+ as acceptable response types. If you need types beyond this, you can register them in your environment:
These routes provide reasonable defaults for many URLs, if you're not using RESTful routing.
NOTE: The default routes will make every action of every controller in your application accessible to GET requests. If you've designed your application to make consistent use of RESTful and named routes, you should comment out the default routes to prevent access to your controllers through the wrong verbs. If you've had the default routes enabled during development, though, you need to be sure that you haven't unwittingly depended on them somewhere in your application - otherwise you may find mysterious failures when you disable them.
Don't confuse the default routes with the empty route. The empty route has one specific purpose: to route requests that come in to the root of the web site. For example, if your site is example.com, then requests to +http://example.com+ or +http://example.com/+ will be handled by the empty route.
TIP: If the empty route does not seem to be working in your application, make sure that you have deleted the file +public/index.html+ from your Rails tree.
If you want a complete list of all of the available routes in your application, run the +rake routes+ command. This will dump all of your routes to the console, in the same order that they appear in +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
* The routing parameters that will be generated by this URL
For example, here's a small section of the +rake routes+ output for a RESTful route:
Routes should be included in your testing strategy (just like the rest of your application). Rails offers three "built-in assertions":http://api.rubyonrails.com/classes/ActionController/Assertions/RoutingAssertions.html designed to make testing routes simpler:
The +assert_recognizes+ assertion is the inverse of +assert_generates+. It asserts that Rails recognizes the given path and routes it to a particular spot in your application.
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+.
