Symfony 7.4 Validate mapped entity when using ObjectMapper with stateOptions

[julian-douma]

Description

When using input: DTO::class with #[Map(target: Entity::class)] and stateOptions: new Options(entityClass: Entity::class), validation only runs on the input DTO. Entity-level constraints like #[UniqueEntity] are never triggered, causing a 500 (DB constraint violation) instead of a proper 422 validation error.

How to reproduce

Entity with UniqueEntity constraint:

#[ORM\Entity]
#[UniqueEntity(fields: ['isbn'], message: 'A book with this ISBN already exists.')]
class Book
{
    #[ORM\Column(type: 'string', length: 13, unique: true)]
    #[Assert\Isbn(type: Assert\Isbn::ISBN_13)]
    private string $isbn;
    
    // ...
}

Input DTO mapped to Entity:

#[Map(target: Book::class)]
final class CreateBookDto
{
    public function __construct(
        #[Assert\NotBlank]
        #[Assert\Isbn(type: Assert\Isbn::ISBN_13)]
        public readonly string $isbn,
        // ...
    ) {}
}

API Resource:

#[ApiResource(
    stateOptions: new Options(entityClass: Book::class),
    operations: [
        new Post(
            uriTemplate: '/books',
            input: CreateBookDto::class,
        ),
    ],
)]
#[Map(source: Book::class)]
class BookResource
{
    // ...
}

Request:

# First request - succeeds
curl -X POST /api/books -d '{"isbn": "9780134685991", ...}'

# Second request with same ISBN - returns 500 instead of 422
curl -X POST /api/books -d '{"isbn": "9780134685991", ...}'

Expected behavior

The #[UniqueEntity] constraint on the Entity should be validated after ObjectMapper maps the DTO to the Entity, returning a 422 validation error.

Actual behavior

• Validation runs on CreateBookDto (passes - no uniqueness check)
• ObjectMapper maps DTO → Book entity
• Entity is persisted → DB throws constraint violation (500)

The #[UniqueEntity] constraint is never evaluated.

Current workaround

Custom processor that manually checks for duplicates:

final class CreateBookProcessor implements ProcessorInterface
{
    public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = []): Book
    {
        $existing = $this->entityManager
            ->getRepository(Book::class)
            ->findOneBy(['isbn' => $data->getIsbn()]);

        if ($existing !== null) {
            throw new DuplicateIsbnException($data->getIsbn());
        }

        $this->entityManager->persist($data);
        $this->entityManager->flush();

        return $data;
    }
}

Possible solution

Since #[Map] already declares the DTO → Entity relationship, validation could automatically run on the mapped entity before persistence. This could be:

1. An option on stateOptions: validateEntity: true
2. Automatic when #[Map(target: Entity::class)] is present on the input DTO
3. A new processor in the chain that validates the entity post-mapping

Environment

• API Platform 4.x
• Symfony 7.x
• Using ObjectMapper for DTO ↔ Entity mapping

Maybe I am doing something wrong?