Cqrs And Handlers (Symfony)

Use when

• Separating writes from reads with distinct command and query buses.
• A service both changes state and returns data for display.
• Adding a use case as a command or a query with its own handler.

Default workflow

1. Name the use case: a command changes state, a query returns data.
2. Write the message as a readonly class and exactly one handler for it.
3. Configure separate command and query buses; give the command bus the validation and doctrine_transaction middleware.
4. Inject the buses behind small interfaces, or the native buses with #[Target].
5. Dispatch from a thin controller and return the query result or the new id.

Guardrails

• Commands return nothing, or at most the id they created.
• Queries have no side effects, so they can be cached and retried.
• One handler per message; no handler dispatches back onto the bus it serves.
• Read models for complex queries are optional: add them when a query outgrows the entities.