PHP 循环删除无限分类子节点

<?php
    private  function _deleteSubNode($ids){

        $subNodes = array();
        $mod = D('Node');
        foreach (explode ( ',', $ids ) as $k){
            $res = $this->_getSubNode($k,$subNodes[$k],$mod);  //获取子节点
            if(!empty($res[0])){
                foreach($res as $k => $nid){
                    $mod->where('id = '.$nid)->delete();       //删除子节点
                }
            }
        }
        return ;
    }

    private function _getSubNode($id, &$arr,$mod){

         $condition = array ('pid' => array ('eq', $id ));
         $ret = $mod->where($condition)->getField('id');
         if(!empty($ret[0])){
             foreach ($ret as $k => $node){
                 $arr[] = $node['id'];
                 $this->_getSubNode($node['id'], $arr, $mod);
            }
         }
         return $arr;
    }

?>

生命只有一次。