Friday Jun 06, 2008

Rails RESTful Resources Tutorial

Today, we published an updated version of the Building a Relationship Between Two Models tutorial. This update takes the RESTful approach to working with has_many relationships, in this case the relationship between a post (the parent) and its comments (the children). REST, which is an acronym for representational state transfer, is an architecture style for hypermedia, such as web applications. By using this architecture, you end up with a simple, uniform way to set up routing for your create-read-update-delete (CRUD) applications, which typically perform the following actions for a resource:

  • List (Index)
  • Create
  • New
  • Show
  • Edit
  • Update
  • Destroy

With RESTful routing, you can use a combination of four HTTP methods (GET, POST, PUT, and DELETE) and four patterns (/controller-name, /controller-name/:id, /controller-name/:id/edit, and /controller-name/new) to formulate the URLs that map to the above actions. For example, for the post resource, you can use the following URLs and HTTP methods:

  • List. /posts + GET
  • Create. /posts + POST
  • New. /posts/new + GET
  • Show. /posts/:id + GET
  • Edit. /posts/:id/edit + GET
  • Update. /posts/:id/ + PUT
  • Destroy. /posts/:id + DELETE

The Rails support for RESTful routing makes this all very easy. When you add a resource to your Rails application, the framework automatically adds to the routes.rb file a map.resource method call that generates the appropriate route mappings to the seven actions, and also creates numerous helper methods for generating paths and urls in string and hash format. Basically, all you have to remember are four substrings:

  • collection, such as posts, for list (index) and create
  • object, such as post, for show, edit, and destroy
  • new_object, such as new_post, for new
  • edit_object, such as edit_post, for edit

For example, to generate the path to invoke the create action, you use new_post_path. To generate the path to invoke the edit action, you use edit_post_path(:id).

In the scenario in the tutorial, where there is a parent-child relationship, you use the Rails nested resources support, which ensures that the comment resources are always accessed in relationship to a post. For example, to generate the path to the create action for comments, you use post_comments_path(:post_id), which generates the URL /posts/:post_id/comments.

The tutorial is a nice way to quickly see RESTful routing in action. If you are interested in learning more about this topic, the tutorial lists several resources that provide in depth explanations of REST architecture and Rails support for this methodology.

Note: I should point out that REST architecture is not simply about URLs and routing. It is a set of constraints that "when applied as a whole, emphasizes scalability of component interactions, generality of interfaces, independent deployment of components, and intermediary components to reduce interaction latency, enforce security, and encapsulate legacy systems." [Roy Fielding, Architectural Styles and the Design of Network-based Software Architectures, Chapter 5, 2000].

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