Rails + Postgres:如何使用多个可能为空的列‘order`？

class CreateOrders < ActiveRecord::Migration[6.0]
  def change
    create_table :orders do |t|
      t.string :name
      t.integer :quantity
      t.decimal :price
      t.integer :order
      t.timestamps
    end
  end
end

class Order < ApplicationRecord
  attribute :order, :integer, default: nil
end

class OrdersController < ApplicationController
  def index
    @orders = Order.all
    @orders.each do |order|
      if order.order.nil?
        # 处理空值的情况
      else
        # 处理非空值的情况
      end
    end
  end
end