Creates named routes for implementing verb-oriented controllers. This is useful for implementing REST API’s, where a single resource has different behavior based on the HTTP verb (method) used to access it.

Example:

  map.resources :messages

  class MessagesController < ActionController::Base
    # GET messages_url
    def index
      # return all messages
    end

    # GET new_message_url
    def new
      # return an HTML form for describing a new message
    end

    # POST messages_url
    def create
      # create a new message
    end

    # GET message_url(:id => 1)
    def show
      # find and return a specific message
    end

    # GET edit_message_url(:id => 1)
    def edit
      # return an HTML form for editing a specific message
    end

    # PUT message_url(:id => 1)
    def update
      # find and update a specific message
    end

    # DELETE message_url(:id => 1)
    def destroy
      # delete a specific message
    end
  end

The resources method sets HTTP method restrictions on the routes it generates. For example, making an HTTP POST on new_message_url will raise a RoutingError exception. The default route in config/routes.rb overrides this and allows invalid HTTP methods for resource routes.

Along with the routes themselves, resources generates named routes for use in controllers and views. map.resources :messages produces the following named routes and helpers:

  Named Route   Helpers
  messages      messages_url, hash_for_messages_url,
                messages_path, hash_for_messages_path
  message       message_url(id), hash_for_message_url(id),
                message_path(id), hash_for_message_path(id)
  new_message   new_message_url, hash_for_new_message_url,
                new_message_path, hash_for_new_message_path
  edit_message  edit_message_url(id), hash_for_edit_message_url(id),
                edit_message_path(id), hash_for_edit_message_path(id)

You can use these helpers instead of url_for or methods that take url_for parameters:

  redirect_to :controller => 'messages', :action => 'index'
  # becomes
  redirect_to messages_url

  <%= link_to "edit this message", :controller => 'messages', :action => 'edit', :id => @message.id %>
  # becomes
  <%= link_to "edit this message", edit_message_url(@message) # calls @message.id automatically

Since web browsers don’t support the PUT and DELETE verbs, you will need to add a parameter ‘_method’ to your form tags. The form helpers make this a little easier. For an update form with a @message object:

  <%= form_tag message_path(@message), :method => :put %>

or

  <% form_for :message, @message, message_path(@message), :html => {:method => :put} do |f| %>

The resources method accepts various options, too, to customize the resulting routes:

• :controller — specify the controller name for the routes.
• :singular — specify the singular name used in the member routes.
• :path_prefix — set a prefix to the routes with required route variables. Weblog comments usually belong to a post, so you might use resources like:

    map.resources :articles
    map.resources :comments, :path_prefix => '/articles/:article_id'
  

  You can nest resources calls to set this automatically:

    map.resources :articles do |article|
      article.resources :comments
    end
  

• :name_prefix — define a prefix for all generated routes, usually ending in an underscore. Use this if you have named routes that may clash.

    map.resources :tags, :path_prefix => '/books/:book_id', :name_prefix => 'book_'
    map.resources :tags, :path_prefix => '/toys/:toy_id',   :name_prefix => 'toy_'
  

• :collection — add named routes for other actions that operate on the collection. Takes a hash of #{action} => #{method}, where method is :get/:post/:put/:delete or :any if the method does not matter. These routes map to a URL like /messages;rss, with a route of rss_messages_url.
• :member — same as :collection, but for actions that operate on a specific member.
• :new — same as :collection, but for actions that operate on the new resource action.

If map.resources is called with multiple resources, they all get the same options applied.

Examples:

  map.resources :messages, :path_prefix => "/thread/:thread_id"
  # --> GET /thread/7/messages/1

  map.resources :messages, :collection => { :rss => :get }
  # --> GET /messages;rss (maps to the #rss action)
  #     also adds a named route called "rss_messages"

  map.resources :messages, :member => { :mark => :post }
  # --> POST /messages/1;mark (maps to the #mark action)
  #     also adds a named route called "mark_message"

  map.resources :messages, :new => { :preview => :post }
  # --> POST /messages/new;preview (maps to the #preview action)
  #     also adds a named route called "preview_new_message"

  map.resources :messages, :new => { :new => :any, :preview => :post }
  # --> POST /messages/new;preview (maps to the #preview action)
  #     also adds a named route called "preview_new_message"
  # --> /messages/new can be invoked via any request method

  map.resources :messages, :controller => "categories",
        :path_prefix => "/category/:category_id",
        :name_prefix => "category_"
  # --> GET /categories/7/messages/1
  #     has named route "category_message"

[Source]

     # File vendor/rails/actionpack/lib/action_controller/resources.rb, line 210
210:     def resources(*entities, &block)
211:       options = entities.last.is_a?(Hash) ? entities.pop : { }
212:       entities.each { |entity| map_resource entity, options.dup, &block }
213:     end