JMS VirtualProperty with argument and custom liste

I am trying to serialize a property which is a Doctrine Criteria:

public function getUserResults(User $user)
{
    $criteria = Criteria::create()
        ->where(Criteria::expr()->eq('user', $user))
    ;

    return $this->getResults()->matching($criteria);
}

I cannot use the @VirtualProperty because it needs an argument so I implemented a custom subscriber for one of my types following this post:

https://stackoverflow.com/a/44244747

<?php

namespace AppBundle\Serializer;

use JMS\Serializer\EventDispatcher\EventSubscriberInterface;
use JMS\Serializer\EventDispatcher\PreSerializeEvent;
use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorage;
use JMS\Serializer\EventDispatcher\ObjectEvent;

class ExerciseSubscriber implements EventSubscriberInterface
{
    private $currentUser;

    public function __construct(TokenStorage $tokenStorage)
    {
        $this->currentUser = $tokenStorage->getToken()->getUser();
    }

    public static function getSubscribedEvents()
    {
        return array(
            array(
                'event' => 'serializer.post_serialize',
                'method' => 'onPostSerialize',
                'class' => Exercise::class, // if no class, subscribe to every serialization
                'format' => 'json', // optional format
            ),
        );
    }

    public function onPostSerialize(ObjectEvent $event)
    {
        if (!$this->currentUser) {
            return;
        }

        $exercise = $event->getObject();
        $visitor = $event->getVisitor();

        $results = $exercise->getUserResults($this->currentUser);
        dump($results); // <-- It is an ArrayCollection with many elements

        $visitor->setData(
            'my_user_results',
            $results // <-- when rendered is an empty {}
        );
    }
}

Unfortunately the user_results property is always empty!
I looked into the source code for the serializer and I found that:

/**
 * Allows you to add additional data to the current object/root element.
 * @deprecated use setData instead
 * @param string $key
 * @param integer|float|boolean|string|array|null $value This value must either be a regular scalar, or an array.
 *                                                       It must not contain any objects anymore.
 */
public function addData($key, $value)
{
    if (isset($this->data[$key])) {
        throw new InvalidArgumentException(sprintf('There is already data for "%s".', $key));
    }

    $this->data[$key] = $value;
}

Please note the It must not contain any objects anymore.

How can I solve this?

Please try to use serializer.post_serialize event instead of serializer.pre_serialize one. Also your virtual property name (user_results) should be different from any existing serializable fields.

The second argument of setData method must either be a regular scalar, or an array. It must not contain any objects. I suggest to inject JMS serializer into your listener class to serialize your objects array into array of scalars.

<?php

namespace AppBundle\Serializer;

use JMS\Serializer\EventDispatcher\EventSubscriberInterface;
use JMS\Serializer\EventDispatcher\PreSerializeEvent;
use Symfony\Component\Security\Core\Authentication\Token\Storage\TokenStorage;
use JMS\Serializer\EventDispatcher\ObjectEvent;
use JMS\Serializer\Serializer;

class ExerciseSubscriber implements EventSubscriberInterface
{
    private $currentUser;
    private $serializer;

    public function __construct(TokenStorage $tokenStorage, Serializer $serializer)
    {
        $this->currentUser = $tokenStorage->getToken()->getUser();
        $this->serializer  = $serializer;
    }

    public static function getSubscribedEvents()
    {
        return array(
            array(
                'event'  => 'serializer.post_serialize',
                'method' => 'onPostSerialize',
                'class'  => Exercise::class, // if no class, subscribe to every serialization
                'format' => 'json', // optional format
            ),
        );
    }

    public function onPostSerialize(ObjectEvent $event)
    {
        if (!$this->currentUser) {
            return;
        }

        $exercise = $event->getObject();
        $visitor = $event->getVisitor();

        $visitor->setData(
            'user_results',
            $this->serializer->toArray($exercise->getUserResults($this->currentUser))
        );
    }
}