带有has_many的counter_cache:通过
我刚刚创建了一个counter_cache字段,控制器看起来像这样。
@users = User.where(:sex => 2).order('received_likes_count')
User.rb中的关联是
has_many :received_likes, :through => :attachments, :source => :likes, :dependent => :destroy
问题是counter_cache是在Like.rb的belongs_to中声明的,我不知道如何告诉它是为了has_many:通过关联。
belongs_to :user, :counter_cache => :received_likes
你以前有过
class Product has_and_belongs_to_many :categories end class Category has_and_belongs_to_many :products end
和迁移
class CreateCategoriesProducts < ActiveRecord::Migration def change create_table :categories_products, id: false do |t| t.references :category t.references :product end add_index :categories_products, [:category_id, :product_id] end end
现在改变所有
class Product has_many :categories_products, dependent: :destroy has_many :categories, through: :categories_products end class Category has_many :categories_products, dependent: :destroy has_many :products, through: :categories_products end
和新的
class CategoriesProduct < ActiveRecord::Base # this model uses table "categories_products" as it is # column products_count is in the table "categories" belongs_to :category, counter_cache: :products_count belongs_to :product end
根据这篇文章 (从上个月)和这篇文章 (从2008年开始),它似乎不可能。 但是,后一篇文章确实有解决方法的代码(为方便起见,从该链接复制/粘贴,在第二个链接中转到DEfusion)
class C < ActiveRecord::Base belongs_to :B after_create :increment_A_counter_cache after_destroy :decrement_A_counter_cache private def increment_A_counter_cache A.increment_counter( 'c_count', self.BAid ) end def decrement_A_counter_cache A.decrement_counter( 'c_count', self.BAid ) end end
(这是针对一个方案,其中C属于B,B属于A,A has_many C:通过=> B
这基本上做同样的事情:
after_save :cache_post_count_on_tags def cache_post_count_on_tags tags.each {|t| tag.update_attribute(:posts_count, t.posts.size)} end
并且您需要有关于标记的posts_count
列,或者您拥有的任何关联。