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Graphql & DataTransformer with Output Entity "No resource class found for object of type [...]"

See original GitHub issue

Hi there!

(using the current 2.4 master)

I have an Entity Class that I want to transform before I return it to the user:

/**
 * @ApiResource(
 *     attributes={"_access_control"="is_granted('ROLE_USER')"},
 *     output=LanguageOutput::class
 * )
 * @ORM\Entity(repositoryClass="App\Repository\LanguageRepository")
 * @UniqueEntity("code")
 */
class Language
{
    /**
     * @ORM\Id()
     * @ORM\GeneratedValue()
     * @ApiProperty(identifier=false)
     * @ORM\Column(type="integer")
     */
    private $id;

    /**
     * @ORM\Column(type="string", length=255, unique=true)
     * @ApiProperty(identifier=true)
     * @Assert\NotBlank()
     */
    private $code;

   // [...]
}

I created a DataTransformer for it:

final class LanguageOutputTransformer implements DataTransformerInterface
{
    /**
     * {@inheritdoc}
     */
    public function transform($data, string $to, array $context = [])
    {
        $parameters = GraphqlQueryParameter::getParametersFromRequest($this->requestStack->getCurrentRequest());

        /** @var Language $data */
        $output = new LanguageOutput(
            $data->getId(),
            $data->getCode(),
            'en'
        );
        return $output;
    }

    /**
     * {@inheritdoc}
     */
    public function supportsTransformation($data, string $to, array $context = []): bool
    {
        return LanguageOutput::class === $to && $data instanceof Language;
    }
}

and created my Output class:

class LanguageOutput
{
    private $id;
    private $in_locale = 'en';
    private $code;

    public function __construct($id, string $code, ?string $in_locale)
    {
        $this->id   = $id;
        $this->code = $code;
        if ($in_locale) {
            $this->in_locale = $in_locale;
        }
    }


    public function getId(): ?int
    {
        return $this->id;
    }

    /**
     * @ApiProperty(identifier=true)
     */
    public function getCode(): ?string
    {
        return $this->code;
    }
}

using this with accept: application/json works just fine - but if I want to query it using graphql, I get

{
  "errors": [
    {
      "debugMessage": "No resource class found for object of type \"App\\Entity\\Dto\\LanguageOutput\".",
      "message": "Internal server error",
      "extensions": {
        "category": "internal"
      },
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "languages"
      ],
      "trace": [
        {
          "file": "/app/src/vendor/api-platform/core/src/Serializer/AbstractItemNormalizer.php",
          "line": 126,
          "call": "ApiPlatform\\Core\\Api\\ResourceClassResolver::getResourceClass(instance of App\\Entity\\Dto\\LanguageOutput, 'App\\Entity\\Dto\\LanguageOutput', true)"
        },
        {
          "file": "/app/src/vendor/api-platform/core/src/Serializer/ItemNormalizer.php",
          "line": 52,
          "call": "ApiPlatform\\Core\\Serializer\\AbstractItemNormalizer::normalize(instance of App\\Entity\\Dto\\LanguageOutput, 'graphql', array(3))"
        },
        {
          "file": "/app/src/vendor/api-platform/core/src/GraphQl/Serializer/ItemNormalizer.php",
          "line": 43,
          "call": "ApiPlatform\\Core\\Serializer\\ItemNormalizer::normalize(instance of App\\Entity\\Dto\\LanguageOutput, 'graphql', array(3))"
        },
[...]

So I tried annotating my LanguageOutput class with @ApiResource, but now graphql returns items of the id /api/language_outputs/[id] - which again cannot be used as id for query or mutation actions, because it refers to a different entity.

Also, I have a set of additional REST endpoints now that I don’t really want.

Is there a correct way to use graphql with a DataTransformerInterface?