public function findByOpenId($openid)
 {
     $select = $this->getDbTable()->select()->where('openid = ?', $openid);
     $row = $this->getDbTable()->fetchRow($select);
     $user = new Default_Model_User();
     $user->setCreated($row->created);
     $user->setId($row->id);
     $user->setUsername($row->username);
     return $user;
 }