ruby-on-rails - 将模块/类中的代码注入(inject)到另一个模块/类中

Question

我想知道将代码从一个模块/类注入(inject)另一个模块/类的常见做法。我有:

module MyModule
  extend ActiveSupport::Concern

  included do
    # The has_many association for Article / Post.
    has_many :comments

    # Here, from MyModule, I would like to "inject" the related belongs_to 
    # association into Comment where the belongs_to association should be
    # 'belongs_to :article' for Article and 'belongs_to :post' for Post.
  end

  module ClassMethods
    # ...
  end
end

class Article < ActiveRecord::Base
  include MyModule
end

class Post < ActiveRecord::Base
  include MyModule
end

class Comment < ActiveRecord::Base
end

要将 belongs_to 关联注入(inject)到 Comment 中，我可以使用 instance_exec 方法，但也许有更聪明的方法。我应该怎么做才能避免代码重复？我应该在 Comment 中 include 其他模块，还是将所有相关代码保留在 MyModule 中，然后从那里注入(inject)？在这些情况下如何进行？

Answer 1

当一个模型属于多个其他模型时，您可以使用 polymorphic associations ，你可以使用 class_eval 来包含一个模块:

module MyModule  
  extend ActiveSupport::Concern  

  included do  
    has_many :comments, as: postable  

    Comment.class_eval do
      include Commentable
    end
  end 

  Module Commentable
    extend ActiveSupport::Concern

    included do
      belongs_to :postable, polymorphic: true
    end

    def ping
      p 'pong'
    end
  end 
end

class Article < ActiveRecord::Base
  include MyModule
end


class Post < ActiveRecord::Base
  include MyModule
end

class Comment < ActiveRecord::Base
end

以非多态的方式，你可以像这样定义包含:

def self.included(base)
  Comment.class_eval do
    belongs_to base.name.underscore # Will result in belongs_to :article and belongs_to :post in this case
  end
end