Rails 3 - 嵌套资源 - 路由

resources :projects do
  resources :tasks
end

project_tasks GET    /projects/:project_id/tasks(.:format)          tasks#index
               POST   /projects/:project_id/tasks(.:format)          tasks#create
new_project_task GET    /projects/:project_id/tasks/new(.:format)      tasks#new
edit_project_task GET    /projects/:project_id/tasks/:id/edit(.:format) tasks#edit
project_task GET    /projects/:project_id/tasks/:id(.:format)      tasks#show
               PATCH  /projects/:project_id/tasks/:id(.:format)      tasks#update
               PUT    /projects/:project_id/tasks/:id(.:format)      tasks#update
               DELETE /projects/:project_id/tasks/:id(.:format)      tasks#destroy

class TasksController< ApplicationController
  before_action :set_project

  def index
    @tasks = @project.tasks
  end

  # ...

  private

  def set_project
    @project = Project.find(params[:project_id])
  end
end