Question

我在posts_count模型中添加了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

现在我正在尝试根据这个问题为他们构建一个计数器缓存（为多对多关联创建一个计数器缓存）：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Post：

时，我得到了这个

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

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

有什么建议吗？

型号：

**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

修改

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入标记模型：

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

您可以将其保留在Post中，但在这种情况下，您必须为所有已分配的标记增加计数器。当post模型已经知道它的标签时（取决于app逻辑），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

但是把这段代码留在Post - 坏主意。更新帖子后你会做什么？根据代码，它将再次增加计数器。添加新标签或删除时，您将做什么：您必须为每个案例编写特殊代码。很糟糕。

Answer 2

HOWTO 仅针对以下帖子递增计数器：status =“已发布”

发布模型：

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

标记模型：

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

如何修复这些increment / decrement_tag_counter_cache方法？

2 个答案: