Ruby on rails 如何使列的最小值为0（或防止减量计数器设置负值）？

我有一个带有

posts\u count

列的标签模型，该列充当一个标签拥有的帖子数量的计数器缓存：

schema.rb:

 t.integer  "posts_count", :default => 0, :null => false

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

  after_save :increment_decrement_tag_counters # covers :save, :create, :update methods

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

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

  def increment_decrement_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

标记。rb:

 t.integer  "posts_count", :default => 0, :null => false

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

  after_save :increment_decrement_tag_counters # covers :save, :create, :update methods

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

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

  def increment_decrement_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

post.rb:

 t.integer  "posts_count", :default => 0, :null => false

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

  after_save :increment_decrement_tag_counters # covers :save, :create, :update methods

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

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

  def increment_decrement_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

现在的问题是，有时，

递减\u标记\u计数器\u缓存

方法会使

posts\u计数

变为负值（例如-1）

有没有办法告诉Rails：将

posts\u count的最小值设为0？因此，如果当前值为0且计数器递减，
posts\u count
仍将保持为0？我可以做的另一件事是防止
递减计数器设置负值。可能吗

（这不应该作为验证工作，而是作为默认行为，因为我不希望出现错误。）
您可以对帖子进行验证，如下所示

validates :posts_count, :numericality => { :greater_than_or_equal_to => 0 }

或者你可以这样做

before_save :set_posts_count

def set_posts_count
  posts_count = 0 if posts_count < 0
end

[posts_count, 0].max

保存前：设置发布次数
def set_posts_计数
如果posts\u count<0，则posts\u count=0
结束
出现问题的原因可能是，据我记忆所及，此方法不会初始化模型实例，因此它会发送一个直接的sql查询，如下所示：

UPDATE "Tags" SET "posts_counter" = COALESCE("posts_counter", 0) - 1 WHERE "Tags"."id" = 5

如果是这样，我不知道如何解决这个问题，可能您可以使用锁初始化模型实例，然后减少计数器，但是锁有它的缺点
您可以这样做

before_save :set_posts_count

def set_posts_count
  posts_count = 0 if posts_count < 0
end

[posts_count, 0].max

因此，如果
decrement\u count
想要使
posts\u count
-1，它将自动变为0，不会出现任何错误（顺便问一下，它不应该是
大于或等于=>0
？同意它应该大于或等于=>0，我不确定是否设置默认值，但你可以做的是进行方法调用，如果posts\u count出现验证错误，将默认值设置为0。这里是另一个选项。这很奇怪，我添加了第一个代码a我还用
-1
得到了
posts\u count
。Muhamamd Awais我甚至尝试了第二个代码：
self.posts\u count=0如果self.posts\u count<0
（我把它放在
tag.rb
）仍然得到了负数。