如何修正这些增量/递减标记_计数器_缓存方法？

Question

我在posts_count模型中添加了一个Tag列：

  create_table "tags", :force => true do |t|
    t.string   "name"
    t.datetime "created_at",                 :null => false
    t.datetime "updated_at",                 :null => false
    t.integer  "posts_count", :default => 0, :null => false
  end

现在，我试图根据这个问题(为多到多的关联创建计数器缓存)为它们构建一个计数器缓存：Counter cache for a model with a many-to-many association。

post.rb:

private

after_create  :increment_tag_counter_cache
after_destroy :decrement_tag_counter_cache

def increment_tag_counter_cache
  Tag.increment_counter(:posts_count, self.taggings.tag.id)
end

def decrement_tag_counter_cache
  Tag.decrement_counter(:posts_count, self.taggings.tag.id)
end

但是当我创建一个Post时，我得到了这个

 undefined method `tag' for []:ActiveRecord::Relation

我认为这个部分有问题：self.taggings.tag.id，但我不太确定如何修复它。

有什么建议吗？

模型：

**post.rb:**

     has_many :taggings, dependent: :destroy  
     has_many :tags, through: :taggings

**tag.rb:**

    has_many :taggings, :dependent => :destroy  
    has_many :posts, :through => :taggings

**tagging:**

    attr_accessible :tag_id, :post_id

    belongs_to :post
    belongs_to :tag

编辑

post.rb:

  before_save :publish_post

  protected

    def publish_post
      if self.status == "Published" && self.published_at.nil?
       self.published_at = Time.now
      end
    end

tagging.rb:

 private

    def increment_tag_counter_cache
      if self.post.status == "Published" && self.post.published_at.nil?
        Tag.increment_counter(:posts_count, self.tag.id)
      end
    end

Answer 1

这个例子有点误导..。

您必须将回调和计数代码放置到标记模型中：

private

after_create  :increment_tag_counter_cache
after_destroy :decrement_tag_counter_cache

def increment_tag_counter_cache
  Tag.increment_counter(:posts_count, self.tag.id)  #
end

def decrement_tag_counter_cache
  Tag.decrement_counter(:posts_count, self.tag.id)
end

您可以将其留在Post中，但在这种情况下，您必须为所有分配的标记增加计数器。当post模型已经知道它的标记(取决于应用程序逻辑)时，必须执行此代码：

def increment_tag_counter_cache
  tags.each do |tag|  # if .tags contain Tag objects... or has_many :tags, :through => :tagggings
    Tag.increment_counter(:posts_count, tag.id)
  end
end

但把这段代码放在后面的坏主意里。更新帖子时，你会做些什么？根据代码，它将再次增加计数器。当您添加新标记或移除时，您将做什么:您必须为每一种情况编写特殊的代码。真没意思。

Answer 2

HOWTO只为具有：=“已发布”的帖子增加计数器

职位模式：

after_save :increment_tag_counters # covers :save, :create, :update methods
before_destroy :correct_tag_counters

def published?
  self.status == "Published"
end

def increment_tag_counters? # if changes provided and previous status wasn't "published"
  status_changed? && changed_attributes["status"] != "Published"
end

def decrement_tag_counters? # if changes provides and previous status was "published"
  status_changed? && changed_attributes["status"] == "Published"
end

def increment_tag_counters
  if published? && increment_tag_counters?
    taggings.each {|tagging| tagging.increment_tag_counter_cache}
  elsif decrement_tag_counters?
    taggings.each {|tagging| tagging.decrement_tag_counter_cache}
  end
end

def correct_tag_counters
  if published?
    taggings.each {|tagging| tagging.decrement_tag_counter_cache}
  end
end

标签模型：

after_create  :increment_tag_counter_cache
after_destroy :decrement_tag_counter_cache

def increment_tag_counter_cache
  Tag.increment_counter(:posts_count, self.tag.id) if post.published?
end

def decrement_tag_counter_cache
  Tag.decrement_counter(:posts_count, self.tag.id) if !post.published? || post.decrement_tag_counters? 
end