public function filterByFirstname($firstname = null, $comparison = null)
    {
        if (null === $comparison) {
            if (is_array($firstname)) {
                $comparison = Criteria::IN;
            } elseif (preg_match('/[\%\*]/', $firstname)) {
                $firstname = str_replace('*', '%', $firstname);
                $comparison = Criteria::LIKE;
            }
        }

        return $this->addUsingAlias(UserPeer::FIRSTNAME, $firstname, $comparison);
    }