Rails has_many通过多态计数器缓存 [英] Rails has_many through polymorphic counter cache

问题描述

我有两个模型，它们通过关联使用多态的has_many链接在一起，我想添加一个counter_cache，但似乎Rails/ActiveRecord不支持此功能.

I have two models I link together using a polymorphic has_many through association and I would like to add a counter_cache but it seems Rails/ActiveRecord does not support this feature out of the box.

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

推荐答案

只需为以下内容修改分类模型:

Simply modify your Classification model for the following:

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

此外，请确保分类表中具有以下列:

Also, make sure you have the following columns in your taxonomies table:

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"更改为所需的内容("answers_count"，"users_count"等)

Change "other_classifiables_count" to what you need ("answers_count", "users_count", etc.)

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