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

Question

我正在尝试“计数器缓存”每个标签中的帖子数量。保存后回调有效，但销毁后无效。看起来 destroy sql 不正确。

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

正确的sql应该是

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

Answer 1

我遇到了完全相同的问题，对我来说，解决方法是在连接表中添加一个主键列(在您的情况下为 PostTag)。

似乎 rails 需要 :dependent => :destroy 的主键工作的选择。