ThinkPHP自动填充实现无限级分类的方法

<?php
class CateAction extends Action{
  function index(){
    $cate=M('cate');
    $list=$cate->field("id,name,pid,path,concat(path,'-',id) as bpath")->order('bpath')->select();
    foreach($list as $key=>$value){
       $list[$key]['count']=count(explode('-',$value['bpath']));
    }
    $this->assign('alist',$list);
    $this->display();  
  }
  //添加栏目
  function add(){
    $cate=new CateModel();
    
    if($vo=$cate->create()){
      if($cate->add()){
        $this->suess('添加栏目成功');  
      }else{
        $this->error('添加栏目失败');  
      }
      //dump($vo);  
    }else{
      $this->error($cate->getError());  
    }
  }
  
}
?>

<?php
class CateModel extends Model{//对应数据库中的表aoli_cate
  protected $_auto=array(
    array('path','tclm',3,'callback'),  
  ); 
  
  function tclm(){
    $pid=isset($_POST['pid'])?(int)$_POST['pid']:0;
    echo ($pid);
    if($pid==0){
      $data=0;
    }else{
      $list=$this->where("id=$pid")->find();
      $data=$list['path'].'-'.$list['id'];//子类的path为父类的path加上父类的id
    }
    return $data;  
  }
}
?>

<form action="__URL__/add" method="post">
 请选择父级栏目<select name="pid" size="20">
         <option value="0">根栏目</option>
         <volist name="alist" id="vo">
          <option value="{$vo['id']}">
            <php>
              for($i=0;$i<$vo['count'];$i++){
                echo '&nbsp;';  
              }
            </php>
            {$vo['name']}
          </option>
         </volist>
        </select><br />
 新的栏目名称<input type="text" name="name" /><br />
 <input type="submit" value="添加栏目" />
</form>