How to get new value in \ApiPlatform\State\ProcessorInterface::process?

[stephanvierkant]

I'm trying to implement our issue tracker into the API Platform (v3) within our Symfony application. Therefor I'm using a DTO and a State Provider and Processor. My Provider is working fine, but I can't get my Processor working.

When I use a patch method, my issue doesn't get updated:

PATCH /api/issues/123
    {
        "state": "Fixed",
    }

returns { "state": "Open"}

Here is my Issue DTO:

<?php
use ApiPlatform\Metadata\ApiResource;
use ApiPlatform\Metadata\Get;
use ApiPlatform\Metadata\GetCollection;
use ApiPlatform\Metadata\Patch;
use Symfony\Component\Serializer\Annotation as Serializer;

#[ApiResource(
    operations: [
        new Get(),
        new GetCollection(),
        new Patch(processor: IssueProcessor::class),
    ],
    normalizationContext: ['groups' => ['issue:read']],
    denormalizationContext: ['groups' => ['issue:read', 'issue:write']],
    provider: IssueProcessor::class,
)]
final class Issue
{
    #[Serializer\Groups(['issue:read', 'issue:write'])]
    private ?string $state = null;
}

And this is my IssueProcessor which is a Provider as well. It fetches and patches my issues from/to the external web service.

I can't understand how to fetch the fields from the PATCH command. $data holds an Issue object with the old data.

<?php
use ApiPlatform\Metadata\CollectionOperationInterface;
use ApiPlatform\Metadata\Operation;
use ApiPlatform\State\ProcessorInterface;
use ApiPlatform\State\ProviderInterface;

final class IssueProcessor implements ProviderInterface, ProcessorInterface
{
    // use HttpClientInterface to get issues from issue tracker
    public function provide(Operation $operation, array $uriVariables = [], array $context = []): object|array|null
    {
        if ($operation instanceof CollectionOperationInterface) {
            return [];
        }

        return new Issue();
    }

    public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = [])
    {
        // where is 'Fixed'?
    }
}

How can I use a DTO to update my Issue?