How to Create your Custom Normalizer

How to Create your Custom Normalizer

The Serializer component uses normalizers to transform any data into an array. The component provides several built-in normalizers but you may need to create your own normalizer to transform an unsupported data structure.

Creating a New Normalizer

Imagine you want add, modify, or remove some properties during the serialization process. For that you’ll have to create your own normalizer. But it’s usually preferable to let Symfony normalize the object, then hook into the normalization to customize the normalized data. To do that, leverage the ObjectNormalizer:

// src/Serializer/TopicNormalizer.php
namespace App\Serializer;

use App\Entity\Topic;
use Symfony\Component\Routing\Generator\UrlGeneratorInterface;
use Symfony\Component\Serializer\Normalizer\ContextAwareNormalizerInterface;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;

class TopicNormalizer implements ContextAwareNormalizerInterface
{
    private $router;
    private $normalizer;

    public function __construct(UrlGeneratorInterface $router, ObjectNormalizer $normalizer)
    {
        $this->router = $router;
        $this->normalizer = $normalizer;
    }

    public function normalize($topic, $format = null, array $context = [])
    {
        $data = $this->normalizer->normalize($topic, $format, $context);

        // Here, add, edit, or delete some data:
        $data['href']['self'] = $this->router->generate('topic_show', [
            'id' => $topic->getId(),
        ], UrlGeneratorInterface::ABSOLUTE_URL);

        return $data;
    }

    public function supportsNormalization($data, $format = null, array $context = [])
    {
        return $data instanceof Topic;
    }
}

Registering it in your Application

Before using this normalizer in a Symfony application it must be registered as a service and tagged with serializer.normalizer. If you’re using the default services.yaml configuration, this is done automatically!

Performance

To figure which normalizer (or denormalizer) must be used to handle an object, the Symfony\Component\Serializer\Serializer class will call the supportsNormalization() (or supportsDenormalization()) of all registered normalizers (or denormalizers) in a loop.

The result of these methods can vary depending on the object to serialize, the format and the context. That’s why the result is not cached by default and can result in a significant performance bottleneck.

However, most normalizers (and denormalizers) always return the same result when the object’s type and the format are the same, so the result can be cached. To do so, make those normalizers (and denormalizers) implement the Symfony\Component\Serializer\Normalizer\CacheableSupportsMethodInterface and return true when hasCacheableSupportsMethod() is called.

Note

All built-in normalizers and denormalizers as well the ones included in API Platform natively implement this interface.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.