code: public function getGroups($uid)
      {
          static $groups = array();
          if (isset($groups[$uid]))
              return $groups[$uid];
  
          $user_groups = \think\Db::name($this->_config['AUTH_GROUP_ACCESS'] . ' a')
              ->where("a.uid='$uid' and g.status='1'")
              ->join($this->_config['AUTH_GROUP'] . ' g' , "a.group_id=g.id")
              ->field('rules')->select();
  
          $groups[$uid] = $user_groups ?: array();
          return $groups[$uid];
      }
docs: 根据用户id获取用户组,返回值为数组
  @param  uid int     用户id
  @return array       用户所属的用户组 array(
  array('uid'=>'用户id','group_id'=>'用户组id','title'=>'用户组名称','rules'=>'用户组拥有的规则id,多个,号隔开'),
  ...)