扶手：如何通过的has_many实施反缓存与自我指涉的多对多：通过 [英] Rails: How to implement counter caching with self-referential Many to Many via has_many :through

问题描述

我如何能推出自己的反缓存使用一种自我指涉的许多一对多的关系，的has_many：通过

我需要跟踪引文和参考文献的数量每篇文章

我使用的大致code，从这个问题的答案<一个href="http://stackoverflow.com/questions/536261/tricky-active-record-relationships-polymorphic-bi-directional-self-referential">question:

 类出版物＆LT;的ActiveRecord :: Base的
  的has_many：引用
  的has_many：cited_publications，：通过=＆GT; ：引用，：源=＆GT; ：参考
  的has_many：引用：foreign_key =＆GT; reference_id：将class_name =＆GT; 引文
  的has_many：refered_publications，：通过=＆GT; ：引用：源=＆GT; ：发布
结束

类引用＆LT;的ActiveRecord :: Base的
  belongs_to的：出版
  belongs_to的：参考：将class_name =＆GT; 发布
结束
 

解决方案

Rails的计数器缓存机制使用的 increment_counter 和 decrement_counter 的内部方法。你应该能够调用从标准的ActiveRecord的回调，这些方法。

像这样的东西应该给你的想法：

 类引用＆LT;的ActiveRecord :: Base的
  belongs_to的：出版
  belongs_to的：参考：将class_name =＆GT; 发布

  after_create：increment_counter_cache
  after_destroy：decrement_counter_cache

  私人
  高清decrement_counter_cache
    Publication.decrement_counter（citations_counter，publication_id）
  结束

  高清increment_counter_cache
    Publication.increment_counter（citations_counter，publication_id）
  结束
 

结束

How can I roll my own counter cache for a self-referential many-to-many relationship that uses has_many :through?

I need to track the number of citations and references for each article

I'm using roughly the code from the answer to this question:

class Publication < ActiveRecord::Base
  has_many :citations
  has_many :cited_publications, :through => :citations, :source => :reference
  has_many :references, :foreign_key => "reference_id", :class_name => "Citation"
  has_many :refered_publications, :through => :references, :source => :publication
end

class Citation < ActiveRecord::Base
  belongs_to :publication
  belongs_to :reference, :class_name => "Publication"
end

解决方案

The Rails counter cache mechanism uses the increment_counter and decrement_counter methods internally. You should just be able to invoke those methods from the standard ActiveRecord callbacks.

Something like this should give you the idea:

class Citation < ActiveRecord::Base
  belongs_to :publication
  belongs_to :reference, :class_name => "Publication"

  after_create  :increment_counter_cache
  after_destroy :decrement_counter_cache

  private
  def decrement_counter_cache
    Publication.decrement_counter("citations_counter", publication_id)
  end

  def increment_counter_cache
    Publication.increment_counter("citations_counter", publication_id)
  end

end

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