Save entity with subresource into redis with Symfony & Api Platform - symfony

Question

I have 2 entities, Event & User. So basically A user can have multiple event.
I have an EventItemDataProvider and in the getItem method I did something like that:
public function getItem(string $resourceClass, $id, string $operationName = null, array $context = []): ?Event
{
if ($event = $this->cache->get($id, Event::class)) {
return $event;
}
$event = $this->em->getRepository(Event::class)->find($id);
if($event) {
$this->cache->set($id, $event, 120);
}
return $event;
}
When the data is returned without the cache I have this result that is correct with the right username:
{
"#context": "/contexts/Event",
"#id": "/events/20",
"#type": "Event",
"title": "new global event 3",
"description": "A big global event 3",
"createdAt": "2019-07-05T09:20:48+00:00",
"owner": {
"#id": "/users/3",
"#type": "User",
"username": "test3"
}
}
But if I hit the same method a second time, it will retrieve the data from the cache (redis) but this time username will be empty like that:
{
"#context": "/contexts/Event",
"#id": "/events/20",
"#type": "Event",
"title": "new global event 3",
"description": "A big global event 3",
"createdAt": "2019-07-05T09:20:48+00:00",
"owner": {
"#id": "/users/3",
"#type": "User",
"username": ""
}
}
Why is my username empty when I retrieve it from redis?
Basically my cache class has these methods:
public function get(string $uniq, string $className)
{
$value = $this->cache->getItem('test_key')->get();
return $value;
}
public function set(string $uniq, object $entity, int $expires = 60)
{
$save = $this->cache->getItem('test_key');
$save->set($entity);
$save->expiresAfter($expires);
$saved = $this->cache->save($save);
return $saved;
}
The owner field in my Event entity:
/**
* #ORM\ManyToOne(targetEntity="App\Entity\User", inversedBy="events")
* #ORM\JoinColumn(nullable=false)
* #Groups({"event:read", "event:write", "event:update"})
* #Assert\Valid()
*/
private $owner;
The username field in my User entity:
/**
* #ORM\Column(type="string", length=25, unique=true)
* #Groups({"user:read", "user:write", "user:update", "event:item:get", "event:update"})
* #Assert\NotBlank(message="Please provide a username")
*/
private $username;
My redis cache configuration:
cache:
app: cache.adapter.redis
default_redis_provider: "redis://redis"
pools:
custom.cache.entity:
adapter: cache.app
default_lifetime: 120
Why my username is filled when I retrieve it from Doctrine Repository but empty when I retrieve it from Redis?
With Xdebug I can see that if I retrieve the data from Doctrine I have something like that:
But if I retrieve the data from the cache I have something like that:
In this second case, initializer -> this seems infinite, so I think that the problem is probably here, but what should I do to solve this issue?