symfony doctrine how to reverse entityManager->persist() - php

Question

I am editing an entity, and upon some manual validation error I want to write a log message to the DB, but when I flush that message, the entity under editing is also flushed to DB. I have tried entityManager->clear() but that throws errors about entity configuration (seems like I need additional cascade configuration on my entities in order to use that).
Is there no simple way of just reversing the entityManager->persist()?
What I want is to be able to NOT persist some of the entities previously called ->persist() on (or fetched from the DB thus automatically being persisted).
Edit function:
public function editAction(Request $request, price $price)
{
$deleteForm = $this->createDeleteForm($price);
$editForm = $this->createForm(\App\Form\priceType::class, $price);
$editForm->handleRequest($request);
if ($editForm->isSubmitted() && $editForm->isValid()) {
//check start before stop
if ( $price->getDateFrom() >= $price->getDateTo()) {
//$this->em->clear(); //not working
$this->helper->flash('fail','Du kan inte sätta prisavtalets startdatum till efter eller samma som dess slutdatum, då skulle det inte tillämpas på någon extraöppning.',$price->getACRGroup());
return $this->render('price/edit.html.twig', array(
'price' => $price,
'edit_form' => $editForm->createView(),
'delete_form' => $deleteForm->createView(),
));
}
And the logging function:
public function flash($type,$message,$unit=null)
{
//REMEMBER when using this logger - use it AFTER your entity work is done (either flushed or $em->clear()
// currently $type can be 'success', 'fail' or 'warning'.
//find out (from services.yaml) if this install is set up to store every message (fails and warnings also) or just success (success means something was changed so always store a log on that)
if (
($type == 'fail' && $this->globalParameters->get('systemlog_save_errors') == 0)
||
($type == 'warning' && $this->globalParameters->get('systemlog_save_warnings') == 0)
) {
return false;
}
if ($type == 'fail') {
$type = 'error';
}
//This is important as the flush() below will otherwise flush ANY ENTITY IN EDIT unless that was explicitly removed from entityManager ( $em->clear() ). DANGER! You will easily and inadvertently save unverified data.
/*
if ($type == 'error') {
$this->em->clear(); //not working
}
*/
//create log entry
$em = $this->em;
$now = new \DateTime("now");
$entity = new Systemlog();
$entity->setACRGroup($unit);
$entity->setemail($this->security->getUser()->getEmail());
$entity->setTime($now);
$entity->setEventType($type);
$entity->setEventMessage($message);
$em->persist($entity);
$em->flush();
}