Doctrine2: PreFlush hook does timeout - doctrine-orm

Question

I have two entities.
First is my Parent entity, that has property called productsCount.
This entity has some another entity linked to it called Store and store have linked Room. Each room can have multiple products in it.
When I edit products that are assigned to room, I want to update the Parent productsCount to store count of all products in all rooms in all stores.
I have a SQL query that does calculate the count. I need to do this each time I update the Room with new products. This is done using preFlush hook using EntityListener on the Room entity.
The preFlush hook gets triggered properly, but then it will timeout for some reason.
Here is the preFlush code example
public function preFlush(Room $room, PreFlushEventArgs $args)
{
$em = $args->getEntityManager();
$parent = $room->getStore()->getParent();
$rsm = new ResultSetMapping();
$rsm->addScalarResult('COUNT(product_id)', 'count');
$query = $em->createNativeQuery(
'select COUNT(product_id)
from room_product where `room_id` in
(select id from room where store_id in
(select id from store where parent_id = :parentId))', $rsm);
$query->setParameter('parentId', $parent->getId());
$result = $query->getOneOrNullResult();
$parent->setNumberOfServices($result['count']);
$em->persist($parent);
$em->flush();
}
The query should be working fine, so I think it has something to do with flushing and persisting the parent entity.
Any ideas?

Answer 1

So, I was able to find a solution after few hours of fighting.
Turns out I dont have to persist, nor flush the changes. The solution is to use Unit of Work to recompute changes on the $parent and then doctrine will flush them by its own. I also had to change the way I count the products, as in the preFlush stage the change is not yet in the database, so the query will not work properly. Thats why I count them manually by traversing the tree of relations.
Here is a code sample.
public function preFlush(Room $room, PreFlushEventArgs $args)
{
$em = $args->getEntityManager();
$numOfProducts = 0;
$parent = $room->getStore()->getParent();
foreach($parent->getStores() as $store) {
foreach($store->getRooms() as $room) {
$numOfServices += count($room->getProducts());
}
}
$parent->setNumberOfProducts($numOfProducts);
$classMetadata = $em->getClassMetadata(get_class($parent));
$em->getUnitOfWork()->computeChangeSet($classMetadata, $parent);
}

Answer 2

The reason is recursion: you're calling $em->flush(); from the subscriber, EntityManager enters flush, fires preFlush event which calls your handler which again calls $em->flush() and so on.
IIRC preFlush is called before change set calculation so just updating your entity with new value should be enough for Doctrine to detect said change.