ruby-on-rails - counter_cache 与 has_many :through

Question

我刚刚创建了一个 counter_cache 字段， Controller 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 belong_to 中声明的，我不知道如何告诉它它是用于 has_many :through 关联。

  belongs_to :user, :counter_cache => :received_likes

Answer 1

你有以前的

    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

现在全部改成

    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