简单的 has_many 关系不保存在 Mongoid 中的父级上

Question

我有以下两个课程

class ProductItem
  include Mongoid::Document
  has_many :variations, class_name: ProductItemVariation, dependent: :destroy
end

class ProductItemVariation
  include Mongoid::Document

  field :name, type: String
  field :price, type: Integer

  belongs_to :item, class_name: ProductItem
  embeds_many :options, class_name: ProductItemVariationOption
end

我像这样设置变体对象：

product_item.variations = square_item[:item_data][:variations].select { |square_variation| square_variation[:item_variation_data][:price_money].present? }.map do |square_variation|
    variation_for_square_item(product_item, square_variation)
end


  def variation_for_square_item(product_item, square_variation)
    data = square_variation[:item_variation_data]
    variation = ProductItemVariation.where(square_id: square_variation[:id]).first || ProductItemVariation.new

    variation.square_id = square_variation[:id]
    variation.version = square_variation[:version]
    variation.name = data[:name]
    variation.price = data[:price_money][:amount]

    variation.options = (data[:item_option_values] || []).map do |square_value|
      ProductItemVariationOption.new(
        option_id: square_value[:item_option_id],
        option_value_id: square_value[:item_option_value_id]
      )
    end

    variation

  end

当我 go 到控制台并输入： ProductItemVariation.first.item时，我看到：

#<ProductItem _id: 602dd549446f223f1ab6767b, created_at: 2021-02-18 02:47:37 UTC, updated_at: 2021-02-18 02:47:37 UTC, square_id: "UHUZZMVWOCS44A6LM3O4UYKT", version: 1613267837045, _type: "ProductItem", _slugs: ["fireside-night"], name: "Fireside Night", description: nil, tax_ids: ["OQ724B7OSUPLCSNQ5LC776MT"], order_online: false, requires_pickup: false, sort_order: 100, category_id: BSON::ObjectId('602dd548446f223f1ab67645'), modifier_list_ids: []>

但是，当我输入： ProductItemVariation.first.item.variations时，我看到一个空数组： []

我错过了什么？ 为什么没有返回该项目的变体？