How to Create your Custom Normalizer
Edit this pageHow 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:
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// src/Serializer/TopicNormalizer.php
namespace App\Serializer;
use App\Entity\Topic;
use Symfony\Component\Routing\Generator\UrlGeneratorInterface;
use Symfony\Component\Serializer\Normalizer\NormalizerInterface;
use Symfony\Component\Serializer\Normalizer\ObjectNormalizer;
class TopicNormalizer implements NormalizerInterface
{
public function __construct(
private UrlGeneratorInterface $router,
private ObjectNormalizer $normalizer,
) {
}
public function normalize($topic, string $format = null, array $context = []): array
{
$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, string $format = null, array $context = []): bool
{
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 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
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.
6.3
The CacheableSupportsMethodInterface
interface is deprecated since Symfony 6.3. You should implement the
getSupportedTypes() method instead, as shown in the section below.
Improving Performance of Normalizers/Denormalizers
6.3
The getSupportedTypes() method was introduced in Symfony 6.3.
Both NormalizerInterface
and DenormalizerInterface
contain a new method getSupportedTypes(). This method allows normalizers or
denormalizers to declare the type of objects they can handle, and whether they
are cacheable. With this info, even if the supports*() call is not cacheable,
the Serializer can skip a ton of method calls to supports*() improving
performance substantially in some cases.
The getSupportedTypes() method should return an array where the keys
represent the supported types, and the values indicate whether the result of
the supports*() method call can be cached or not. The format of the
returned array is as follows:
- The special key
objectcan be used to indicate that the normalizer or denormalizer supports any classes or interfaces. - The special key
*can be used to indicate that the normalizer or denormalizer might support any types. - The other keys in the array should correspond to specific types that the normalizer or denormalizer supports.
- The values associated with each type should be a boolean indicating if the
result of the
supports*()method call for that type can be cached or not. A value oftruemeans that the result is cacheable, whilefalsemeans that the result is not cacheable. - A
nullvalue for a type means that 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 result is not cacheable
MyCustomClass::class => true, // Supports MyCustomClass and result is cacheable
];
}
}Note that supports*() method implementations should not assume that
getSupportedTypes() has been called before.
