public function generate(XmlEntityManager $xem, $xmlEntity)
{
$className = get_class($xmlEntity);
// keep a file marker on the filesystem with the "next" number in it
// $db = $xem->getDocumentDatabase($className);
// $coll = $dm->getDocumentCollection($className);
//
// $query = array('_id' => $coll->getName());
// $newObj = array('$inc' => array('current_id' => 1));
//
// $command = array();
// $command['findandmodify'] = 'doctrine_increment_ids';
// $command['query'] = $query;
// $command['update'] = $newObj;
// $command['upsert'] = true;
// $command['new'] = true;
// $result = $db->command($command);
// return $result['value']['current_id'];
}