screen/application/common/model/GoodsInstallLink.php

<?php

namespace app\common\model;

use think\db\Query;
use think\Model;

/**
 * @property GoodsInstall install
 */
class GoodsInstallLink extends Model
{
    public function scopeSku(Query $query,$sku_id,$goods_id=null){
        $query->where('goods_sku_id',$sku_id);
        if($goods_id){
            $query->where('goods_id',$goods_id);
        }
    }
    public function install(){
        return $this->belongsTo(GoodsInstall::class);
    }

    public static function getFee($sku_id,$num){
        $installLink=self::where('goods_sku_id',$sku_id)->with(['install'])->find();
        $fee=0;
        if($installLink){
            $install=$installLink->install;
            $fee=$install->getFee($num);
        }
        return $fee;
    }
}