Doctrine - how to get scalars hydrated to the related children level - php

Question

i'm trying to get from the database some Tasks with the count of contents (related to task) and the assignment objects (related to task) with the count of answers (related to assignment).
So I'm using scalars for the counts and it's pretty fine but I cannot manage to have one count_of_answers by assignments...
Here if my entities relationships :
class Task
{
/**
* #ORM\OneToMany(targetEntity="App\Entity\Assignment", mappedBy="task", orphanRemoval=true)
*/
private $assignments;
/**
* #ORM\OneToMany(targetEntity="App\Entity\Content", mappedBy="task", orphanRemoval=true)
*/
private $contents;
}
class Content
{
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Task", inversedBy="contents")
* #ORM\JoinColumn(nullable=false)
*/
private $task;
/**
* #ORM\OneToMany(targetEntity="App\Entity\Answer", mappedBy="content", orphanRemoval=true)
*/
private $answers;
}
class Assignment
{
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Task", inversedBy="assignments")
* #ORM\JoinColumn(nullable=false)
*/
private $task;
/**
* #ORM\OneToMany(targetEntity="App\Entity\Answer", mappedBy="assignment", orphanRemoval=true)
*/
private $answers;
}
class Answer
{
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Content", inversedBy="answers")
* #ORM\JoinColumn(nullable=false)
*/
private $content;
/**
* #ORM\ManyToOne(targetEntity="App\Entity\Assignment", inversedBy="answers")
* #ORM\JoinColumn(nullable=false)
*/
private $assignment;
}
I would like to get in one query (I think this is possible to avoid querying inside a loop) something like :
Array [[
Task1{
properties,
assignments [
Assignment1{
properties,
count_of_answers
},
Assignment2{
properties,
count_of_answers
},...
]
},
count_of_contents
],
[
Task2{},
count_of_contents
],...
]
So i tried this query in my task repository :
$r = $this->createQueryBuilder('t')
->innerJoin('t.assignments', 'a')
->addSelect('a')
->innerJoin('t.contents', 'c')
->addSelect('COUNT(DISTINCT c.id) AS count_of_contents')
->leftJoin('a.answers', 'an')
->addSelect('COUNT(DISTINCT an.id) AS count_of_answers')
->groupBy('a.id')
->getQuery()
->getResult();
But it's giving something like :
Array[[
Task1{}
count_of_contents,
count_of_answers
],
Task2{}
count_of_contents,
count_of_answers
]]
Could you please help ?
Maybe I should use DQL with a subquery but I'm affraid to lose performence in the sql side. I believe the data fetched are good (when I try the sql query, I do have one count_of_answers by assignment), but the hydratation is not correctly mapped and I only get the last count_of_answers associated to the task instead of assignment.