Expand multiple collections of an entity in Doctrine - php

Question

I'm writing a Symfony application, and I am facing a problem with Doctrine entities eager loading.
I'm not sure if I can load multiple one to many collections on the same entity instance while keeping good performance.
There are many examples on the internet with people load one entity and one of its relationships.
Ex :
$user = $em->createQuery('
select a, au
from OctiviTestBundle:Article a
left join a.authorList au
where a.id = ?1')
->setParameter(1, $id)
->getOneOrNullResult();
However if I also want to load the article comments, the following request retrieves too many results (nb authors * nb comments) => combinatory explosion
$user = $em->createQuery('
select a, au
from OctiviTestBundle:Article a
left join a.authorList au
left join a.commentList c
where a.id = ?1')
->setParameter(1, $id)
->getOneOrNullResult();
In fact, I found no way to reuse an object once it has been loaded from the database. I don't know how to make a second query to load more parts of it later.
Eg :
$user = $em->createQuery('
select a, au
from OctiviTestBundle:Article a
left join a.authorList au
where a.id = ?1')
->setParameter(1, $id)
->getOneOrNullResult();
$em->LoadRelation($user, 'commentList');
$em->LoadRelation($user, 'commentList.author')
$em->LoadRelation($user, 'commentList.author.school');
... load any relation I want, while keeping only one root object.
I would like to be able to have only the main entity instance variable, eager load its 2 relationships and then go through the hierarchy.
I know I can load the two lists in different php variables, but I'd like to only pass the "$user" variable to the view template.
Do you have ideas about how to resolve this issue ?
Thanks
The only (tricky) solution I found is on this website : https://tideways.io/profiler/blog/5-doctrine-orm-performance-traps-you-should-avoid
1) Load the related entities
$companies = array_map(function($employee) {
return $employee->getCompany();
}, $employees);
$repository = $entityManager->getRepository('Acme\Company');
$repository->findBy(['id' => $companies]);
2) Don't use the result (drop the $companies variable), but now Doctrine has got the results in cache, so when I do $employee->getCompany()->getName(), it should not generate new queries.
=> Doesn't work : Doctrine doesn't put the results in the cache to reuse them later.

Answer 1

If the result is always going to be massive no matter what where's and ands you put in, and if you have no intent on doing any write operations on the result you should fetch them as an array instead of as the default objects.
The resulting array is still used exactly the same within twig however as you no longer have to hydrate the objects your memory saving will be huge.