api-resource Skill

Creating API Platform Resources

Design-First Principle

An API Platform resource is built from three concerns (see https://api-platform.com/docs/core/design/):

1. Resource declaration — a plain PHP object marked #[ApiResource] describing the public shape. Single source of truth for Hydra, OpenAPI and GraphQL.
2. Data retrieval — a state provider hydrates that object (Get, GetCollection).
3. Data persistence — a state processor writes it (Post, Put, Patch, Delete).

Design the public shape first; the resource class doesn't have to be a Doctrine entity. How you wire it to persistence is a separate decision:

Approach	When	Hookup
Entity as Resource	Prototyping, plain CRUD, internal model == public shape	#[ApiResource] on the entity; built-in Doctrine provider/processor (zero wiring)
DTO with Object Mapper	Decoupled public shape over a Doctrine entity/document — whether fields match 1:1 or need renames/transforms	stateOptions: new Options(entityClass:/documentClass:) and #[Map] on the DTO
Input DTOs per Operation	Write model differs from read model (stricter create/update payloads)	per-operation input: + processor
Custom Provider/Processor	Non-CRUD, external data, complex domain logic, CQRS	hand-written ProviderInterface/ProcessorInterface (see state-provider/state-processor)

Rule of thumb: entity-as-resource is convenient but couples your public contract to your schema — fine for prototypes, probably not for large or non-CRUD systems. Decouple with a DTO as soon as the two shapes diverge.

Entity as Resource (Simplest)

Mark the entity itself — built-in Doctrine providers/processors handle everything. No provider, processor, or mapping to write:

use ApiPlatform\Metadata\ApiResource;
use Doctrine\ORM\Mapping as ORM;

#[ORM\Entity]
#[ApiResource]
class Book
{
    #[ORM\Id, ORM\GeneratedValue, ORM\Column]
    public ?int $id = null;

    #[ORM\Column]
    public string $title = '';
}

Use this for prototypes and straight CRUD. Migrate to a DTO (strategies below) once the API shape must differ from the schema.

DTO with Object Mapper (Recommended)

One mechanism, not two: API Platform's ObjectMapperProvider / ObjectMapperProcessor activate only when both are present — stateOptions naming the entityClass: (or documentClass:) and a #[Map] attribute on the DTO (and on the input entity for writes). On read it runs map($entity, $resourceClass); on write map($inputDto, $entityClass) then persists via the Doctrine processor. There is no Object-Mapper mode without stateOptions.

Fields that line up by name map automatically; add #[Map(source: …)] to rename or transform: to convert. The same config covers both the trivial 1:1 case and arbitrary renames/transforms:

<?php
namespace App\ApiResource;

use ApiPlatform\Doctrine\Odm\State\Options;
use ApiPlatform\Metadata\ApiResource;
use ApiPlatform\Metadata\Get;
use ApiPlatform\Metadata\GetCollection;
use App\Document\Order as DocumentOrder;
use App\Transformer\CustomerTransformer;
use Symfony\Component\ObjectMapper\Attribute\Map;

#[ApiResource(
    operations: [
        new Get(stateOptions: new Options(documentClass: DocumentOrder::class)),
        new GetCollection(stateOptions: new Options(documentClass: DocumentOrder::class)),
    ]
)]
#[Map(target: DocumentOrder::class)]
final class Order
{
    public string $id;

    // Simple 1:1 field mapping (automatic when names match)
    public string $status;

    // Map from a different source field
    #[Map(source: 'customerName')]
    public string $buyer;

    // Transform with a custom callable
    #[Map(source: 'rawData', transform: new CustomerTransformer())]
    public CustomerDto $customer;
}

Custom Transformers

Implement TransformCallableInterface for complex mappings:

<?php
namespace App\Transformer;

use Symfony\Component\DependencyInjection\Attribute\Exclude;
use Symfony\Component\ObjectMapper\TransformCallableInterface;

#[Exclude]
final class CustomerTransformer implements TransformCallableInterface
{
    public function __construct(private readonly string $field = 'name') {}

    public function __invoke(mixed $value, object $source, ?object $target): mixed
    {
        // $value = source field value, $source = full source object
        $dto = new CustomerDto();
        $dto->name = $value[$this->field] ?? '';
        return $dto;
    }
}

Use #[Exclude] so Symfony's container doesn't try to autowire transformer constructor args.

Input DTOs per Operation

When the write model differs from the read model, give individual operations their own input: DTO and processor (the resource class stays the read model):

#[ApiResource(
    operations: [
        new Post(input: CreateOrderInput::class, processor: OrderCreateProcessor::class),
        new Patch(input: UpdateOrderInput::class, processor: OrderUpdateProcessor::class),
    ]
)]
class Order { /* read model */ }

Nested Sub-Resources with uriVariables

For resources nested under parents (e.g., /accounts/{accountId}/mailboxes/{mailboxId}/messages):

#[ApiResource(
    operations: [
        new Get(
            uriTemplate: '/accounts/{accountId}/mailboxes/{mailboxId}/messages/{id}',
            uriVariables: ['accountId', 'mailboxId', 'id'],
            stateOptions: new Options(
                handleLinks: MessageLinkHandler::class,
                documentClass: Message::class,
            )
        ),
        new GetCollection(
            uriTemplate: '/accounts/{accountId}/mailboxes/{mailboxId}/messages',
            uriVariables: ['accountId', 'mailboxId'],
            stateOptions: new Options(
                handleLinks: MessageLinkHandler::class,
                documentClass: Message::class,
            ),
            itemUriTemplate: '/accounts/{accountId}/mailboxes/{mailboxId}/messages/{id}',
        ),
    ]
)]

The handleLinks class validates parent ownership and applies security filters. See the securing-collections skill for implementation details.

Hidden IRI fields for URI generation:

#[ApiProperty(readable: false, writable: false)]
#[Map(source: 'account', transform: new DocumentIdTransformer())]
public string $accountId;

Custom Named Operations

Add non-CRUD actions on the same resource:

new Put(
    uriTemplate: '/orders/{id}/cancel',
    input: CancelOrderInput::class,
    processor: OrderCancelProcessor::class,
    name: '_api_order_cancel',
),
new Get(
    write: true, // triggers processor on GET
    uriTemplate: '/orders/{id}/download',
    processor: OrderDownloadProcessor::class,
    name: '_api_order_download',
),

Use write: true on Get operations that need a processor (e.g., file downloads): a Get's write phase is off by default, so the processor never fires until you flip the flag. See operations → Read & write phases for the read/write lifecycle.

Backed Enums

As a property

A backed enum property serializes to its ->value automatically:

#[ApiResource]
class Person
{
    public GenderType $genderType; // backed enum → {"genderType": "female"}
}

As a resource

Expose a backed enum as a read-only resource so clients can discover allowed values:

use ApiPlatform\Metadata\ApiResource;

#[ApiResource]
enum AvailabilityStatus: string
{
    case InStock = 'InStock';
    case OutOfStock = 'OutOfStock';
}

GET /availability_statuses lists all cases; GET /availability_statuses/InStock returns one.

High-Precision Numbers

For monetary/scientific values that must avoid float drift, type a property as \BcMath\Number (PHP 8.4 native, requires ext-bcmath). It serializes as a string to preserve precision:

class Invoice
{
    public ?\BcMath\Number $total; // → "300.55"
}

Laravel (Eloquent)

The design-first split, DTOs, Object Mapper, per-operation input:, nested uriVariables/handleLinks, custom operations and backed-enum resources all work on Laravel. Deltas:

• Model as resource: #[ApiResource] on a class extending Illuminate\Database\Eloquent\Model; the Eloquent provider/processor handle CRUD with zero wiring.
• Eloquent Options (ApiPlatform\Laravel\Eloquent\State\Options) uses modelClass: (not entityClass:/documentClass:); it carries modelClass + handleLinks only — no repositoryMethod.
• Object Mapper is supported: pair stateOptions: new Options(modelClass: ProductModel::class) with #[Map(source: ProductModel::class)] on the DTO; per-property #[Map] and TransformCallableInterface are identical.
• Properties: Eloquent models have no typed properties, so declare #[ApiProperty] at the class level with property: (#[ApiProperty(property: 'title', identifier: true)]). DTO/ApiResource classes use property-level attributes. \BcMath\Number and backed enums behave the same.

Checklist

When creating a new resource:

• Create the DTO class in src/ApiResource/
• Add #[ApiResource] with operations
• Define provider for read operations (or use stateOptions)
• Define processor for write operations
• Add validation constraints to input DTOs
• For nested resources: configure uriVariables and handleLinks
• Add #[Map] attributes for entity/document mapping
• Add #[ApiProperty] for OpenAPI documentation