Contributed by Mathias Arlaud
in #43973.

The Serializer component allows you to pass some context information to the
serializing and deserializing process. For example, to ignore certain attributes
when serializing, you can use the following code:

$serializer->serialize($person, 'json', ['ignored_attributes' => ['age']]);

// Symfony also defines public constants for the names of all context options
$serializer->serialize($person, 'json', [AbstractNormalizer::IGNORED_ATTRIBUTES => ['age']]);

In Symfony 6.1 we're improving the definition of serialization contexts with the
introduction of Context Builders. Instead of having to deal with plain arrays,
these objects allow you to define the context using a fluent interface which
provides autocompletion, validation and documentation.
As shown in this example, you can mix both arrays and builder objects and you
can even merge these context objects between them:

use Symfony\Component\Serializer\Context\Encoder\CsvEncoderContextBuilder;
use Symfony\Component\Serializer\Context\Normalizer\ObjectNormalizerContextBuilder;

$initialContext = [
'custom_key' => 'custom_value',
];

$contextBuilder = (new ObjectNormalizerContextBuilder())
->withContext($initialContext)
->withGroups(['group1', 'group2']);

$contextBuilder = (new CsvEncoderContextBuilder())
->withContext($contextBuilder)
->withDelimiter(';');

$serializer->serialize($something, 'csv', $contextBuilder->toArray());

If you need the context as a plain array (e.g. to pass it to serialize()
method) call to the toArray() method:

$this->serializer->serialize($data, 'csv', $contextBuilder->toArray());

When building your own context builder, consider using the
Symfony\Component\Serializer\Context\ContextBuilderTrait to reuse some
common methods:

// src/Serializer/LegacyContextBuilder
namespace App\Serializer;

use Symfony\Component\Serializer\Context\ContextBuilderInterface;
use Symfony\Component\Serializer\Context\ContextBuilderTrait;

final class LegacyContextBuilder implements ContextBuilderInterface
{
use ContextBuilderTrait;

public function withNullableDates(bool $nullable = true): static
{
return $this->with('zero_datetime_to_null', $nullable);
}
}

// you can now use this context builder as follows:
// $context = (new LegacyContextBuilder())->withNullableDates();

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