cxinv/app/admin/model/InvoicePool.php

<?php
declare (strict_types = 1);

namespace app\admin\model;

use think\Model;

/**
 * @mixin \think\Model
 */
class InvoicePool extends Model
{

    public function PoolInfo(){
        return $this->belongsTo(InvoicePoolInfo::class,'invNo','invNo')->bind(["buyer_code","seller_code"]);
    }
}