ruby-on-rails - Rails 查询包括不工作

Question

在我的应用程序中，我有 3 个模型:Item、Category 和 Categorization，定义如下:

class Item < ActiveRecord::Base
  attr_accessible :name, :description

  has_many :categorizations
  has_many :categories, :through => :categorizations
end

class Category < ActiveRecord::Base
  attr_accessible :name, :description, :parent, :children, :items, :parent_id  

  has_many :children, :class_name => "Category", :foreign_key => "parent_id", :dependent => :nullify
  belongs_to :parent, :class_name => "Category"

  has_many :categorizations
  has_many :items, :through => :categorizations
end

class Categorization < ActiveRecord::Base
  attr_accessible :category, :item

  belongs_to :category
  belongs_to :item

end

但是，这样做:

 Category.where(:parent_id => self.id).includes(:items)

不会返回与该类别关联的项目。我在这里缺少什么？

Answer 1

试试这个:

Category.where(parent_id: id).joins(:items)