Question

我有两个模型，我通过关联使用多态has_many链接在一起，我想添加一个counter_cache但似乎Rails / ActiveRecord不支持开箱即用的这个功能。

class Classifiable < ActiveRecord::Base
  has_many :classifications, :as => :classifiable, :foreign_key => :classifiable_id
end

class Taxonomy < ActiveRecord::Base
  has_many :classifications, :as => :taxonomy, :foreign_key => :taxonomy_id
end

class Question < Classifiable
  has_many :categories, :through => :classifications, :as => :classifiable, :source => :taxonomy, :source_type => "Category"
end

class Category < Taxonomy
  has_many :questions, :through => :classifications, :source => :classifiable, :source_type => "Question"
end

class Classification < ActiveRecord::Base
  attr_accessible :classifiable, :classifiable_id, :classifiable_type,
                  :taxonomy, :taxonomy_id, :taxonomy_type

  belongs_to :classifiable, :polymorphic => true
  belongs_to :taxonomy,     :polymorphic => true
end

Answer 1

只需修改以下分类模型：

class Classification < ActiveRecord::Base
  attr_accessible :classifiable, :classifiable_id, :classifiable_type,
                  :taxonomy, :taxonomy_id, :taxonomy_type

  belongs_to :classifiable, :polymorphic => true
  belongs_to :taxonomy,     :polymorphic => true

  before_create  :increment_counter
  before_destroy :decrement_counter

  private

  # increments the right classifiable counter for the right taxonomy
  def increment_counter
    self.taxonomy_type.constantize.increment_counter("#{self.classifiable_type.downcase.pluralize}_count", self.taxonomy_id)
  end

  # decrements the right classifiable counter for the right taxonomy
  def decrement_counter
    self.taxonomy_type.constantize.decrement_counter("#{self.classifiable_type.downcase.pluralize}_count", self.taxonomy_id)
  end
end

另外，请确保分类表中包含以下列：

t.integer :questions_count,           :null => false, :default => 0
t.integer :other_classifiables_count, :null => false, :default => 0
t.integer :other_classifiables_count, :null => false, :default => 0
t.integer :other_classifiables_count, :null => false, :default => 0

将“other_classifiables_count”更改为您需要的内容（“answers_count”，“users_count”等）

Answer 2

看起来Rails在调用delete时没有通过before / after_destroy回调（当你删除一个有多个关联时会发生什么）。

相反，您可以使用关联的回调#before_add和#before_remove：

class Question < Classifiable
  has_many :categories, through: :classifications, 
                        as: :classifiable, 
                        source: :taxonomy, 
                        source_type: Category,
                        before_add: :increment_counter

  def increment_counter(category)
    # increment counter, etc.
  end

end

Answer 3

要稍微修改Jonathan的答案，你可以让它在增量/减量之前查找列类型以查看它是否存在。我也把它干掉了一点：

def increment_counter(direction=:increment)
  ar_class  = self.taxonomy_type.constantize
  ar_column = "#{self.taxonomy_type.underscore.pluralize}_count"

  if ar_class.columns.include? ar_column
    ar_class.send "#{direction}_counter", ar_column, self.taxonomy_id
  end
end

def decrement_counter
  increment_counter :decrement
end

哦，它适用于MultiWordClassNames。 underscore执行了downcase，因此我的版本省略了它。

Rails has_many通过多态计数器缓存

3 个答案: