PHP学习：PHP两种实现无级递归分类的方法

/**
* 无级递归分类 TP框架
* @param int $assortPid 要查询分类的父级id
* @param mixed $tag  上下级分类之间的分隔符
* @return string $tree 返回的分类树型结构结果 
*
*/
function recursiveAssort($assortPid, $tag = '')
{ 
 $assort = M('goods_class')->where("class_pid = $assortPid")->field('class_id, class_name')->select();
 foreach ($assort as $value) {
 $tree .= '<option value="' . $value['class_id'] . '">' . $tag . $value['class_name'] . '</option>';
 $tree .= recursiveAssort($value['class_id'], $tag . ' ');
 }
 return $tree;
}

/**
 * 利用php的引用传递 CI框架
 *
 */
 public function get_access()
 {
 $access = array();
 $field = 'id, pid, method, name, description';
 $q_access = $this->db->select($field)->get('access');
 $q_result = $q_access->result_array();
 if (!empty($q_result)) {
  $items = array();
  foreach ($q_result as $value) {
  $items[$value['id']] = $value;
  }
  foreach ($items as $key => $item) {
  if ($item['pid'] == 0) {
   $access[] = &$items[$key];
  } else {
   $items[$item['pid']]['sub_access'][] = &$items[$key];
  }
  }
 }
 return $access;
 }