What you can do is this:
public function fetchByLoginFromMaster($login)
{
  $conn = ProjectConfiguration::getActive()->getMasterConnection();
  $q = Doctrine_Query::create($conn)
                ->from('User')
                ->where('login = ?', $login)
                ->fetchOne();
  return $q;
}
                  johnwards
                   2010-07-05 15:46:57