Api Platform State Providers (Symfony)

Use when

• Reading data from a source other than the default Doctrine provider.
• Wrapping the Doctrine provider to post-process results (return a DTO, enforce a tenant scope).
• Business logic must run before or after persisting (hashing, slug, dispatching a message).
• A v4 read endpoint must dispatch a query or command through a processor.

Default workflow

1. Implement ProviderInterface::provide() returning iterable|object|null, where null gives a 404 (v3.4 declares mixed).
2. To keep Doctrine fetching, inject api_platform.doctrine.orm.state.item_provider and api_platform.doctrine.orm.state.collection_provider with #[Autowire].
3. Implement ProcessorInterface::process() and delegate to api_platform.doctrine.orm.state.persist_processor or remove_processor.
4. Wire them with provider: and processor: on the resource or the operation; autoconfiguration registers them, and the api_platform.state_provider or api_platform.state_processor tag is only needed without it.
5. For a processor on GET or GetCollection, add write: true (v4 only).