/**
 * Retrieve object using using composite pkey values.
 * @param      int $usergroup_id
   @param      int $user_id
   
 * @param      PropelPDO $con
 * @return     UsergroupHasChief
 */
 public static function retrieveByPK($usergroup_id, $user_id, PropelPDO $con = null)
 {
     $key = serialize(array((string) $usergroup_id, (string) $user_id));
     if (null !== ($obj = UsergroupHasChiefPeer::getInstanceFromPool($key))) {
         return $obj;
     }
     if ($con === null) {
         $con = Propel::getConnection(UsergroupHasChiefPeer::DATABASE_NAME, Propel::CONNECTION_READ);
     }
     $criteria = new Criteria(UsergroupHasChiefPeer::DATABASE_NAME);
     $criteria->add(UsergroupHasChiefPeer::USERGROUP_ID, $usergroup_id);
     $criteria->add(UsergroupHasChiefPeer::USER_ID, $user_id);
     $v = UsergroupHasChiefPeer::doSelect($criteria, $con);
     return !empty($v) ? $v[0] : null;
 }