How to Create your Custom Normalizer

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, you can inject a NormalizerInterface and wire it to Symfony's object normalizer. This will give you access to a $normalizer property which takes care of most of the normalization process:

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

use App\Entity\Topic;
use Symfony\Component\DependencyInjection\Attribute\Autowire;
use Symfony\Component\Routing\Generator\UrlGeneratorInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;

class TopicNormalizer implements NormalizerInterface
{
    public function __construct(
        #[Autowire(service: 'serializer.normalizer.object')]
        private readonly NormalizerInterface $normalizer,

        private UrlGeneratorInterface $router,
    ) {
    }

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

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

        return $data;
    }

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

    public function getSupportedTypes(?string $format): array
    {
        return [
            Topic::class => true,
        ];
    }
}

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!

If you're not using autoconfigure, you have to tag the service with serializer.normalizer. You can also use this method to set a priority (higher means it's called earlier in the process):

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# config/services.yaml
services:
    # ...

    App\Serializer\TopicNormalizer:
        tags:
            # register the normalizer with a high priority (called earlier)
            - { name: 'serializer.normalizer', priority: 500 }

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<!-- config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        https://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <!-- ... -->

        <service id="App\Serializer\TopicNormalizer">
            <!-- register the normalizer with a high priority (called earlier) -->
            <tag name="serializer.normalizer"
                priority="500"
            />
        </service>
    </services>
</container>

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// config/services.php
namespace Symfony\Component\DependencyInjection\Loader\Configurator;

use App\Serializer\TopicNormalizer;

return function(ContainerConfigurator $container) {
    // ...

    // if you're using autoconfigure, the tag will be automatically applied
    $services->set(TopicNormalizer::class)
        // register the normalizer with a high priority (called earlier)
        ->tag('serializer.normalizer', [
            'priority' => 500,
        ])
    ;
};

Improving Performance of Normalizers/Denormalizers

Both :class:Symfony\\Component\\Serializer\\Normalizer\\NormalizerInterface and :class:Symfony\\Component\\Serializer\\Normalizer\\DenormalizerInterface define a getSupportedTypes() method to declare which types they support and whether their supports*() result can be cached.

This does not cache the actual normalization or denormalization result. It only caches the decision of whether a normalizer supports a given type, allowing the Serializer to skip unnecessary supports*() calls and improve performance.

The getSupportedTypes() method should return an array where the keys represent the supported types, and the values indicate whether the result of the corresponding supports*() call can be cached. The array format is as follows:

1. The special key object can be used to indicate that the normalizer or denormalizer supports any classes or interfaces.
2. The special key * can be used to indicate that the normalizer or denormalizer might support any type.
3. Other keys should correspond to specific types that the normalizer or denormalizer supports.
4. The values should be booleans indicating whether the result of the supports*() call for that type is cacheable. Use true if the result can be cached, false if it cannot.
5. A null value means the normalizer or denormalizer does not support that type.

Here is an example of how to use the getSupportedTypes() method:

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use Symfony\Component\Serializer\Normalizer\NormalizerInterface;

class MyNormalizer implements NormalizerInterface
{
    // ...

    public function getSupportedTypes(?string $format): array
    {
        return [
            'object' => null,             // doesn't support any classes or interfaces
            '*' => false,                 // supports any other types, but the decision is not cacheable
            MyCustomClass::class => true, // supports MyCustomClass and decision is cacheable
        ];
    }
}