Indirect modification of overloaded element of api\life\model\NewsModel has no effect

最近遇到了一个这样的问题。

起因是我的代码：

$user['order']=$order->alias('a')

    ->join('shop w','a.pid = w.id','left')
    ->where('a.userid',$data['id'])
    ->field('a.*,w.pic')
    ->select();
foreach ($user['order'] as $k=>$v){
　　$user['order'][$k]['pic']=$this->img($v['pic']);

}
然后我查了下资料，是说在循环中产生的，要设置一个中间变量。
修改如下:

$user['order']=$order->alias('a')
    ->join('shop w','a.pid = w.id','left')
    ->where('a.userid',$data['id'])
    ->field('a.*,w.pic')
    ->select();
$res=$user['order'];
foreach ($res as $k=>$v){
    $v['pic']=$this->img($v['pic']);
    $res[$k]=$v;
}
$user['order']=$res;