在中我們知道，頁面提交給web伺服器的請求先是嘗試直接查詢並返回public目錄中的資源，如果沒有找到則將請求交給Rails的Routes。Routes根據路由配置，將請求轉化為對Controller中的Action並呼叫之。Routes的配置可說的細節很多，最開始我們先關注三種最簡單的方式：Simple route,Default route,Root route。Routes的配置資訊存放在config/routes.rb檔案當中。

當前我的routes.rb檔案如下所示，大段被註釋掉的內容是各種配置用法的舉例先不用理會，其中第二行get "demo/index"這句就是在《Ruby on Rails，建立最簡單的檢視/控制器單元Hello World

在Routes配置檔案中，越靠上的一行配置擁有越高的優先順序。

SimpleSite::Application.routes.draw do
  get "demo/index"

  # The priority is based upon order of creation:
  # first created -> highest priority.

  # Sample of regular route:
  #   match 'products/:id' => 'catalog#view'
  # Keep in mind you can assign values other than :controller and :action

  # Sample of named route:
  #   match 'products/:id/purchase' => 'catalog#purchase', :as => :purchase
  # This route can be invoked with purchase_url(:id => product.id)

  # Sample resource route (maps HTTP verbs to controller actions automatically):
  #   resources :products

  # Sample resource route with options:
  #   resources :products do
  #     member do
  #       get 'short'
  #       post 'toggle'
  #     end
  #
  #     collection do
  #       get 'sold'
  #     end
  #   end

  # Sample resource route with sub-resources:
  #   resources :products do
  #     resources :comments, :sales
  #     resource :seller
  #   end

  # Sample resource route with more complex sub-resources
  #   resources :products do
  #     resources :comments
  #     resources :sales do
  #       get 'recent', :on => :collection
  #     end
  #   end

  # Sample resource route within a namespace:
  #   namespace :admin do
  #     # Directs /admin/products/* to Admin::ProductsController
  #     # (app/controllers/admin/products_controller.rb)
  #     resources :products
  #   end

  # You can have the root of your site routed with "root"
  # just remember to delete public/index.html.
  # root :to => 'welcome#index'

  # See how all your routes lay out with "rake routes"

  # This is a legacy wild controller route that's not recommended for RESTful applications.
  # Note: This route will make all actions in every controller accessible via GET requests.
  # match ':controller(/:action(/:id))(.:format)'
end
 

match "demo/index", :to => "demo#index"

這種路由配置最簡單易懂但是比較不易於維護，因為我們要在每次增加檢視/控制器時維護Routes配置。我們想使用一個更加通用的規則，在這個規則的幫助下我們修改檢視/控制器規則後依然能夠工作-Default route。

get /:controller/:action/:id的意思是呼叫名為demo的Controller中名為index的Action並傳入id值。

match ':controller(/:action(/:id(.:format)))'
 

SimpleSite::Application.routes.draw do
  match ':controller(/:action(/:id))(.:format)'
end

修改了routes.rb之後需要重啟伺服器。請求“localhost:3000/demo/index”依然能夠轉向之前的頁面，說明Default route配置包含了之前Simple route的情況。

由於我們之前刪除了public目錄中的index.html，所以當以“localhost:3000/”請求時將沒有規則能夠匹配“/”。

這時，我們需要配置Root route。

root :to => "demo#index"

SimpleSite::Application.routes.draw do
  root :to => "demo#index"  
  match ':controller(/:action(/:id))(.:format)'
end