screen/application/common/service/InstallService.php

<?php
namespace app\common\service;

use app\common\model\GoodsInstallLink;

class InstallService{
    /**
     * sku_id=>[num=>1,]
     */
   public static function getFee($goods,$numKey='num_install'){
       $fee=0;
       foreach ($goods as $sku_id=>$info){
           $fee=bcadd($fee,GoodsInstallLink::getFee($sku_id,$info[$numKey]));
       }
       return $fee;
   }
}