erp/app/Models/BusinessOrderItem.php

<?php

namespace App\Models;

class BusinessOrderItem extends Model
{
    /**
     * 不可批量赋值的属性。为空则所有熟悉都可以批量赋值
     *
     * @var array
     */
    protected $guarded = [];

    public function order()
    {
        return $this->hasOne(BusinessOrder::class, 'id', 'business_order_id');
    }
}