ruby-on-rails - 具有父引用的 Mongoid 为空

Question

我正在尝试做 Model Tree Structures with Parent References使用 Mongoid，
但是 parent 设置为 null。

这是我的课:

class Category
  include Mongoid::Document
  field :name, type: String
  belongs_to :parent, :class_name => 'Category'
end

这就是我创建类别的方式:

parent = Category.new(name: "Mobile").save!
child1 = Category.new(name: "Android", parent: parent).save!
child2 = Category.new(name: "iOS", parent: parent).save!

结果:

{ 
    "categories": [
        {
            "_id": "511b84c5cff53e03c6000126",
            "name": "Mobile",
            "parent_id": null,
        },
        {
            "_id": "511b84c5cff53e03c6000128",
            "name": "Android",
            "parent_id": null,
        },
        {
            "_id": "511b84c5cff53e03c6000129",
            "name": "iOS",
            "parent_id": null,
        }
    ]
}

父级甚至没有存储在数据库中:

{ "name" : "Mobile",  "_id" : "511b84c5cff53e03c6000126" }
{ "name" : "Android", "_id" : "511b84c5cff53e03c6000128" }
{ "name" : "iOS",     "_id" : "511b84c5cff53e03c6000129" }

哪里做错了？

谢谢!
荣荣

Answer 1

除了声明 belongs_to 关联之外，您还需要声明相反的 has_many 关联，即使它在同一个类中也是如此。

class Category
  include Mongoid::Document
  field :name, type: String

  has_many :children,
    class_name: 'Category',
    inverse_of: :parent
  belongs_to :parent,
    class_name: 'Category',
    inverse_of: :children
end

您可以通过关联分配 parent 或 child 。

parent = Category.create
child1 = Category.create
child2 = Category.create

parent.children << child1
parent.children << child2

然后子级将存储对父级的引用。