API Platform 4 Resources

Prefer DTO resources over exposing entities

Exposing a Doctrine entity directly as #[ApiResource] couples your public API to your schema and leaks persistence concerns. For anything beyond a trivial CRUD prototype, expose a DTO resource backed by a state provider (read) and state processor (write).

// ✅ GOOD — a resource DTO, decoupled from the entity
#[ApiResource(
    shortName: 'Order',
    operations: [
        new Get(provider: OrderItemProvider::class),
        new GetCollection(provider: OrderCollectionProvider::class),
        new Post(processor: CreateOrderProcessor::class, input: CreateOrderInput::class),
    ],
    normalizationContext: ['groups' => ['order:read']],
)]
final class OrderResource
{
    public function __construct(
        #[ApiProperty(identifier: true)]
        #[Groups(['order:read'])]
        public string $id,

        #[Groups(['order:read'])]
        public string $status,

        /** @var LineItemResource[] */
        #[Groups(['order:read'])]
        public array $items = [],
    ) {}
}

// ❌ BAD — Doctrine entity as the API resource: schema is now your public contract
#[ApiResource]
#[ORM\Entity]
class Order { /* every column auto-exposed, lazy associations serialized, N+1 */ }

If you do expose entities (small internal apps), always scope fields with serialization groups and disable the operations you don't want.

State processors (write side)

A processor receives the input DTO and performs the use case — usually by delegating to an application service / Messenger bus.

// ✅ GOOD
/** @implements ProcessorInterface<CreateOrderInput, OrderResource> */
final class CreateOrderProcessor implements ProcessorInterface
{
    public function __construct(private readonly OrderService $orders) {}

    public function process(mixed $data, Operation $operation, array $uriVariables = [], array $context = []): OrderResource
    {
        $order = $this->orders->createOrder($data);   // $data is the validated CreateOrderInput

        return OrderResource::fromEntity($order);
    }
}

State providers (read side)

// ✅ GOOD — provider returns the read model, not the entity
/** @implements ProviderInterface<OrderResource> */
final class OrderItemProvider implements ProviderInterface
{
    public function __construct(private readonly OrderRepository $orders) {}

    public function provide(Operation $operation, array $uriVariables = [], array $context = []): ?OrderResource
    {
        $order = $this->orders->find(Uuid::fromString($uriVariables['id']));

        return $order ? OrderResource::fromEntity($order) : null;
    }
}

Use the built-in Pagination in collection providers; don't return unbounded arrays.

Validation

Put Symfony Validator constraints on the input DTO. API Platform validates automatically before the processor runs and returns RFC 9457 problem+json on failure.

final class CreateOrderInput
{
    #[Assert\NotBlank]
    #[Assert\Email]
    public string $customerEmail;

    /** @var CreateLineInput[] */
    #[Assert\Valid]
    #[Assert\Count(min: 1)]
    public array $items = [];
}

Operations & security

• Declare operations explicitly; don't accept the default full CRUD set unless you mean it.
• Authorize per-operation with security:

new Post(security: "is_granted('ROLE_USER')"),
new Delete(security: "is_granted('ORDER_DELETE', object)"),  // voter on the object

Filters & pagination

#[ApiResource(
    operations: [new GetCollection()],
    paginationItemsPerPage: 20,
    paginationMaximumItemsPerPage: 100,
)]
#[ApiFilter(SearchFilter::class, properties: ['status' => 'exact', 'customerEmail' => 'partial'])]
#[ApiFilter(OrderFilter::class, properties: ['createdAt' => 'DESC'])]
final class OrderResource { /* ... */ }

For large datasets, see doctrine-query-optimization — switch collection providers to keyset pagination.

Versioning & errors

• Version through the path prefix or a vendor media type; keep order:read / order:write groups stable.
• Don't hand-build error responses — API Platform emits RFC 9457 problem+json (see problem-details-rfc9457). Throw domain exceptions mapped to status codes.

Gotchas

• Agent slaps #[ApiResource] on a Doctrine entity — prefer a DTO resource with provider/processor for non-trivial APIs.
• Agent leaves all CRUD operations enabled by default — declare only the operations you intend to expose.
• Agent forgets serialization #[Groups] — every property gets exposed, including sensitive ones.
• Agent puts business logic in the processor — delegate to an application service; the processor just adapts.
• Agent returns the entity from a provider — return the resource DTO.
• Agent disables pagination or returns findAll() from a collection provider — keep pagination on.
• Agent hand-rolls error JSON — let API Platform produce problem+json; throw mapped exceptions.
• Agent uses API Platform 2/3 annotations (@ApiResource) — use PHP 8 attributes and the v4 metadata classes (ApiPlatform\Metadata\*).