ActiveRecord - has_many:through,:dependent =>:destroy sql不正确

Question

我试图"反缓存"每个标签中的帖子数量.后保存回调正在工作,但后毁灭不是.看起来像破坏sql是不正确的.

class Post < ActiveRecord::Base
  has_many :post_tags, :dependent => :destroy
  has_many :tags, :through => :post_tags
end

class Tag < ActiveRecord::Base
  has_many :post_tags, :dependent => :destroy
  has_many :posts, :through => :post_tags
end

class PostTag < ActiveRecord::Base
  self.table_name =  :posts_tags
  belongs_to :post
  belongs_to :tag

  after_save :update_tag_posts_count
  after_destroy :update_tag_posts_count

  def update_tag_posts_count
    tag.posts_count = tag.posts.count
    tag.save
  end
end

测试失败

# @tag.posts_count == 10
Failure/Error: @tag.posts.first.destroy 
ActiveRecord::StatementInvalid:
 Mysql2::Error: Unknown column 'posts_tags.' in 'where clause': DELETE FROM `posts_tags` WHERE `posts_tags`.`` = NULL

应该是正确的sql

DELETE FROM `posts_tags` WHERE `posts_tags`.`post_id` = {the post id}

Answer 1

我建议单独的递增/递减函数，而不是使用计数+保存。这应该正常工作，表现良好，不会触发标签的副作用，并且不会在竞争条件下弄乱你的计数。

class PostTag < ActiveRecord::Base

  belongs_to :post
  belongs_to :tag

  after_create  :increment_tag_posts_counter
  after_destroy :decrement_tag_posts_counter

  private

  def increment_tag_posts_counter
    Tag.increment_counter :posts_count, post_id
  end

  def decrement_tag_posts_counter
    Tag.decrement_counter :posts_count, post_id
  end
end