ruby on rails-带有父引用的Mongoid为null

Question

我正在尝试使用Mongoid使用父引用创建模型树结构，
但是父级被设置为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,
        }
    ]
}

父项甚至没有存储在DB:中

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

我做错了什么？

谢谢
Roei

Answer 1

除了声明belongs_to关联之外，还需要声明相反的has_many关联，即使它在同一个类上。

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

您可以通过关联来分配父级或子级。

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。

Answer 2

最终，当我单独保存时（与创建不在同一行），它就起了作用。

之前（不能正常工作）：

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

之后（工作！）：

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

结果（如预期）：

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

非常感谢所有响应者！