class Order < ApplicationRecord
         has_many  :items
         accepts_nested_attributes_for :items
    end

class Item < ApplicationRecord


belongs_to  :order

end

{
  "location": "takeAway",
  "status": "preparing",
  "items": [
    {
        "id":2,
      "name": "coffee",
      "quantity": 1,
      "milk": "whole",
      "size": "small"
    }
  ]
}

params.require(:order).permit(:location, :status, items_attributes:  [:id, :name, :quantity, :milk, :size])