عرض عملي: إعادة تصميم تجمّع Order

خطوة بخطوة

1. Start from the setter-based Order and a service with if (status == ...) checks.
2. Introduce OrderId, Money, and OrderLine value types; remove setters.
3. Move rules into methods: addLine, place, cancel, with status transitions.
4. Raise OrderPlaced and OrderCancelled events and publish them from the application service after save.
5. Planned mistake: hold a full Customer object inside Order. Replace it with CustomerId and explain why loading and locking grew.
6. Write one unit test per invariant, with no Spring context.