[TYPO3-mvc] filter for frontend user in isValid validator

[Domi]

Ok found out little bit more:

> But the sql output brings:
> TYPO3\\CMS\\Extbase\\Domain\\Model\\FrontendUser

All values must getting update with single "\". Then the findByUid find 
my record.

But findByUsername was not successful, maybe because of the matter of 
Pid. How can I disable just for this query. I tried with my own query 
but not successful:

$query = $this->frontendUserRepository->createQuery();
		$query->getQuerySettings()->setRespectStoragePage(false);
$query->matching($query->equals('username', $username));
$result = $query->execute();

Is there any good tool, how I can see now how the pure sql looks like?

Or better: How can I tell FrontendUser which pid is used?

Thanks a lot for your quick help

Dominic