JMS Serializer Subscriber example with Symfony 4.4

App\Controller\Api\ProductController.php

<?php

namespace App\Controller\Api;

use App\Repository\ProductRepository;
use FOS\RestBundle\Controller\AbstractFOSRestController;
use FOS\RestBundle\View\View;
use Symfony\Component\HttpFoundation\Response;
use FOS\RestBundle\Controller\Annotations as Rest;

/**
 * @Rest\Route("/product")
 */
class ProductController extends AbstractFOSRestController
{
    /**
     * @var ProductRepository
     */
    private ProductRepository $repository;

    /**
     * ProductController constructor.
     * @param ProductRepository $repository
     */
    public function __construct(ProductRepository $repository)
    {
        $this->repository = $repository;
    }

    /**
     * @Rest\Get("/")
     * @Rest\View(serializerGroups={"Default", "product_stock"})
     *
     * @return View
     */
    public function getAction(): View
    {
        $products = $this->repository->findAll();

        return View::create($products, Response ::HTTP_OK);
    }
}

App\Entity\Product.php

<?php

namespace App\Entity;

use Doctrine\ORM\Mapping as ORM;
use JMS\Serializer\Annotation as Serializer;

/**
 * @ORM\Entity(repositoryClass="App\Repository\ProductRepository")
 * @Serializer\ExclusionPolicy("all")
 */
class Product
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ORM\Column(type="integer")
     * @Serializer\Expose()
     */
    private int $id;

    /**
     * @ORM\Column(type="string", length=255)
     * @Serializer\Expose()
     */
    private string $name;

    /**
     * @ORM\Column(type="string", length=255)
     */
    private string $brand;

    /**
     * @ORM\Column(type="float", options={"default":0})
     */
    private float $price;

    public function getId(): int
    {
        return $this->id;
    }

    public function getName(): string
    {
        return $this->name;
    }

    public function setName(string $name): self
    {
        $this->name = $name;

        return $this;
    }

    public function getBrand(): string
    {
        return $this->brand;
    }

    public function setBrand(string $brand): self
    {
        $this->brand = $brand;

        return $this;
    }

    public function getPrice(): float
    {
        return $this->price;
    }

    public function setPrice(float $price): self
    {
        $this->price = $price;

        return $this;
    }
}

App\Serializer\Subscriber\ProductSubscriber.php

<?php

namespace App\Serializer\Subscriber;

use App\Entity\Product;
use App\Util\BrandType;
use App\Util\OffPrice;
use JMS\Serializer\Context;
use JMS\Serializer\EventDispatcher\EventSubscriberInterface;
use JMS\Serializer\EventDispatcher\ObjectEvent;
use JMS\Serializer\JsonSerializationVisitor;
use JMS\Serializer\Metadata\StaticPropertyMetadata;

class ProductSubscriber implements EventSubscriberInterface
{

    /**
     * Returns the events to which this class has subscribed.
     *
     * Return format:
     *     array(
     *         array('event' => 'the-event-name', 'method' => 'onEventName', 'class' => 'some-class', 'format' => 'json'),
     *         array(...),
     *     )
     *
     * The class may be omitted if the class wants to subscribe to events of all classes.
     * Same goes for the format key.
     *
     * @return array
     */
    public static function getSubscribedEvents()
    {
        return [
            [
                'event' => 'serializer.post_serialize',
                'method' => 'onPostSerialize',
                'class' => Product::class,
                'format' => 'json',
            ],
        ];
    }

    /**
     * @param Context $context
     * @param string $group
     *
     * @return bool
     */
    private function isGroupActive(Context $context, string $group): bool
    {
        $groups = $context->hasAttribute('groups') ? $context->getAttribute('groups') : [];

        return in_array($group, $groups);
    }

    /**
     * @param JsonSerializationVisitor $visitor
     * @param string $key
     * @param $value
     */
    private function addData(JsonSerializationVisitor $visitor, string $key, $value)
    {
        $visitor->visitProperty(new StaticPropertyMetadata('', $key, $value), $value);
    }

    /**
     * @param ObjectEvent $event
     * @throws \ReflectionException
     */
    public function onPostSerialize(ObjectEvent $event)
    {
        /** @var Product $product */
        $product = $event->getObject();
        $context = $event->getContext();

        /** @var JsonSerializationVisitor $visitor */
        $visitor = $event->getVisitor();

        // Add brand node
        $this->addData($visitor, 'brand', [
            'id' => $product->getBrand(),
            'name' => BrandType::getName($product->getBrand()),
        ]);

        // Add price node
        $this->addData($visitor, 'price', OffPrice::getPrice($product->getBrand(), $product->getPrice()));

        // Add stock node
        if ($this->isGroupActive($context, 'product_stock')) {
            $this->addData($visitor, 'stock', 100);
        }
    }
}

response_example.txt

//GET /api/product/
[
  {
    "id": 1,
    "name": "Product Name 1",
    "brand": "Brand Name 1", //<-- node added by default from `ProductSubscriber`
    "price": "99.99", //<-- node added by default from `ProductSubscriber`
    "stock": 100 //<-- node added from `ProductSubscriber` if `product_stock` serialization group is used
  }
]