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Routing Concerns 允許您宣告常見路由，可供其他資源和路由重複使用。

concern :commentable do
  resources :comments
end

concern :image_attachable do
  resources :images, only: :index
end

這些 concern 應用於 Resources 路由

resources :messages, concerns: [:commentable, :image_attachable]

或範疇或名稱空間

namespace :posts do
  concerns :commentable
end
方法
C

執行個體公開方法

concern(name, callable = nil, &block)

定義路由 concern 並使用一個名稱。

Concerns 可使用區塊內嵌定義，或透過將該物件傳遞為第二個參數，交由另一個物件處理。

若有提供 concern 物件，該物件應回應 call，其將會收到兩個參數

* The current mapper
* A hash of options which the concern object may use

也可以使用 concern 定義區塊內接受區塊參數，如此將會限制特定資源上可用的動作，傳遞標準資源選項以透過 concern 傳遞

concern :commentable do |options|
  resources :comments, options
end

resources :posts, concerns: :commentable
resources :archived_posts do
  # Don't allow comments on archived posts
  concerns :commentable, only: [:index, :show]
end

或者，透過使用可呼叫物件，您能夠針對應用程式實作更特定功能，該功能在路徑檔案內會不適當。

# purchasable.rb
class Purchasable
  def initialize(defaults = {})
    @defaults = defaults
  end

  def call(mapper, options = {})
    options = @defaults.merge(options)
    mapper.resources :purchases
    mapper.resources :receipts
    mapper.resources :returns if options[:returnable]
  end
end

# routes.rb
concern :purchasable, Purchasable.new(returnable: true)

resources :toys, concerns: :purchasable
resources :electronics, concerns: :purchasable
resources :pets do
  concerns :purchasable, returnable: false
end

任何路由輔助工具皆可使用於 concern 內部。如果使用可呼叫工具，則可從傳遞至 call 的 Mapper 存取。

程式碼：顯示 | GitHub 上

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 2145
def concern(name, callable = nil, &block)
  callable ||= lambda { |mapper, options| mapper.instance_exec(options, &block) }
  @concerns[name] = callable
end

concerns(*args)

使用命名 concern

resources :posts do
  concerns :commentable
end

Concerns 也適用於您想使用的任何路由輔助工具

namespace :posts do
  concerns :commentable
end

程式碼：顯示 | GitHub 上

# File actionpack/lib/action_dispatch/routing/mapper.rb, line 2161
def concerns(*args)
  options = args.extract_options!
  args.flatten.each do |name|
    if concern = @concerns[name]
      concern.call(self, options)
    else
      raise ArgumentError, "No concern named #{name} was found!"
    end
  end
end