xPDO query question

$zip = 12345;
$c = $modx->newQuery('modUser');
$c->select($modx->getSelectColumns('modUser','modUser','',array('id','username')));
$c->innerJoin('modUserProfile','Profile');
$c->where(array(
    'Profile.zip' => $zip,
    'modUser.active' => true,
));
$users = $modx->getCollection('modUser',$c);

$list = array();
foreach ($users as $user) {
   $list[$user->get('id')] = $user->get('username');
}

$users = $modx->getCollectionGraph('modUser',array('Profile' => array()),$c);