Union response type not working

[WouterCypers]

Q	A
Bug report?	yes
Feature request?	no
BC Break report?	no
RFC?	no
Version/Branch	1.0.0

I have a mutation ResetPassword which should return some date OR an error response. The response is defined as a Union. I get an error when executing the mutation:

Abstract type ResetPasswordResponse must resolve to an Object type at runtime for field publicMutation.ResetPassword with value "instance of App\GraphQL\PublicApi\Mutation\ResetPassword\ResetPasswordMutationFailedResponse", received "null". Either the ResetPasswordResponse type should provide a "resolveType" function or each possible type should provide an "isTypeOf" function.

In the documentation, I only see resolveType or isTypeOf being used for interfaces. I'm not sure how to make this work.

The GraphQL request:

mutation resetPassword {
  ResetPassword (
    input: {
      token: "PasswordResetRequest-011eaf33-a93a-4f72-9509-e2b739741535"
      newPassword: "MyPassword01!+qw121124"
      repeatNewPassword: "MyPassword01!+qw12112"
    }
  ) {
    ... on ResetPasswordSuccessfulResponse {
      token
      newPassword
    }
    ... on ResetPasswordFailedResponse {
      errors
    }
  }
}

The mutation:

      ResetPassword:
        type: ResetPasswordResponse
        resolve: '@=mutation("reset_password", args["input"]["token"], args["input"]["newPassword"], args["input"]["repeatNewPassword"])'
        args:
          input:
            type: ResetPasswordInput!

The resolver:

class ResetPasswordMutation implements MutationInterface, AliasedInterface
{
    public function __construct(
        private MessageBusInterface $messageBus,
    ) {}

    public function resetPassword(
        string $token,
        string $newPassword,
        string $repeatNewPassword
    ): ResetPasswordMutationResponse {
        try {
            $this->messageBus->dispatch(
                new ResetPassword(
                    $token,
                    $newPassword,
                    $repeatNewPassword
                )
            );
            return new ResetPasswordMutationSuccessfulResponse($token, $newPassword);
        } catch (ValidationFailedException $exception) {
            $violations = [];
            /** @var ConstraintViolationInterface $violation */
            foreach ($exception->getViolations() as $violation) {
                $violation->getMessage();
            }
            return new ResetPasswordMutationFailedResponse($violations);
        }
    }

    public static function getAliases(): array
    {
        return [
            'resetPassword' => 'reset_password',
        ];
    }
}

YAML types config:

ResetPasswordResponse:
  type: union
  config:
    types: [ResetPasswordSuccessfulResponse, ResetPasswordFailedResponse]
    description: 'Reset password succeeded or failed.'

ResetPasswordSuccessfulResponse:
  type: object
  config:
    fields:
      token:
        type: 'String!'
      newPassword:
        type: 'String!'

ResetPasswordFailedResponse:
  type: object
  config:
    fields:
      errors:
        type: '[String]'

[murtukov]

@WouterCypers you should use union types exactly like interfaces. You can check the documentation for interfaces for more details.

In your case you should define for your abstract type (ResetPasswordResponse) a type resolver (resolveType):

ResetPasswordResponse:
  type: union
  config:
    types: [ResetPasswordSuccessfulResponse, ResetPasswordFailedResponse]
    description: 'Reset password succeeded or failed.'
    resolveType: "@=query('map_response_type', value, typeResolver)"

And modify your ResetPasswordMutation class:

use GraphQL\Type\Definition\ObjectType;
use Overblog\GraphQLBundle\Resolver\TypeResolver;
use Overblog\GraphQLBundle\Resolver\UnresolvableException;

class ResetPasswordMutation implements MutationInterface, AliasedInterface
{
    public function __construct(
        private MessageBusInterface $messageBus,
    ) {}

    public function resetPassword(
        string $token,
        string $newPassword,
        string $repeatNewPassword
    ): ResetPasswordMutationResponse {
        try {
            $this->messageBus->dispatch(
                new ResetPassword(
                    $token,
                    $newPassword,
                    $repeatNewPassword
                )
            );
            return new ResetPasswordMutationSuccessfulResponse($token, $newPassword);
        } catch (ValidationFailedException $exception) {
            $violations = [];
            /** @var ConstraintViolationInterface $violation */
            foreach ($exception->getViolations() as $violation) {
                $violation->getMessage();
            }
            return new ResetPasswordMutationFailedResponse($violations);
        }
    }

    public function mapResponseType($value, TypeResolver $typeResolver): ObjectType
    {
        if ($value instanceof ResetPasswordMutationSuccessfulResponse) {
            return $typeResolver->resolve('ResetPasswordSuccessfulResponse');
        } 
    
        if ($value instanceof ResetPasswordMutationFailedResponse) {
            return $typeResolver->resolve('ResetPasswordFailedResponse');
        }

        throw new UnresolvableException("Couldn't resolve type for union 'ResetPasswordResponse'");
    }

    public static function getAliases(): array
    {
        return [
            'resetPassword' => 'reset_password',
            'mapResponseType' => 'map_response_type'
        ];
    }
}