Add extra fields using JMS Serializer bundle

Question

I've an entity I usually serialize using the JMS Serializer bundle. I have to add to the serialization some fields that doesn't reside in the entity itself but are gathered with some db queries.

My idea was to create a custom object, fill the fields with the entity fields and add the custom one. But this seems a bit tricky and expensive to do for every variation (I use lot of serialization groups) of the class.

Is there a better/standard way to do this? Using a factory? Pre/Post serialization events?

Maybe I can listen for the serialization and checking entity type and serialization groups add the custom fields? But instead of making a query for each entity it would be better to gather all the data of the related entities and then add it to them. Any help is appreciated

Answer 1

I've found the solution by myself,

to add a custom field after the serialization has been done we've to create a listener class like this:

<?php

namespace Acme\DemoBundle\Listener;

use JMS\DiExtraBundle\Annotation\Service;
use JMS\DiExtraBundle\Annotation\Tag;
use JMS\DiExtraBundle\Annotation\Inject;
use JMS\DiExtraBundle\Annotation\InjectParams;
use Symfony\Component\HttpKernel\Event\PostResponseEvent;
use Acme\DemoBundle\Entity\Team;
use JMS\Serializer\Handler\SubscribingHandlerInterface;
use JMS\Serializer\EventDispatcher\EventSubscriberInterface;
use JMS\Serializer\EventDispatcher\PreSerializeEvent;
use JMS\Serializer\EventDispatcher\ObjectEvent;
use JMS\Serializer\GraphNavigator;
use JMS\Serializer\JsonSerializationVisitor;

/**
 * Add data after serialization
 *
 * @Service("acme.listener.serializationlistener")
 * @Tag("jms_serializer.event_subscriber")
 */
class SerializationListener implements EventSubscriberInterface
{

    /**
     * @inheritdoc
     */
    static public function getSubscribedEvents()
    {
        return array(
            array('event' => 'serializer.post_serialize', 'class' => 'Acme\DemoBundle\Entity\Team', 'method' => 'onPostSerialize'),
        );
    }

    public function onPostSerialize(ObjectEvent $event)
    {
        $event->getVisitor()->addData('someKey','someValue');
    }
}

That way you can add data to the serialized element.

Instead, if you want to edit an object just before serialization use the pre_serialize event, be aware that you need to already have a variable (and the correct serialization groups) if you want to use pre_serialize for adding a value.