3. Tactical DDD

Inside a BoundedContext, we define the detailed domain model.

Aggregates and Entities

BoundedContext Checkout {
  Aggregate OrderAgg {
    owner "CheckoutTeam"

    Entity Order {
      aggregateRoot // Marks the aggregate root
      - OrderId id
      Money totalamount
      OrderStatus status

      def void addItem(ProductItem item);
    }

    ValueObject OrderId { String value key }
    ValueObject Money { BigDecimal amount String currency }

    enum OrderStatus { CREATED, PAID, SHIPPED, CANCELLED }
  }
}

• Syntax:
  • Types: String, int, boolean, Date, etc. or custom types.
  • References: Use - before the type (e.g., - CustomerId customer).
  • Methods: def ReturnType methodName(ArgType arg);

Services and Repositories

BoundedContext Checkout {
  Aggregate OrderAgg {
    // ... entities ...

    Repository OrderRepository {
      @Order save(@Order order);
      @Order findById(@OrderId id);
    }

    Service OrderProcessingService {
      void processPendingOrders();
    }
  }
}

• Repository: Interface for persistence, usually linked to an Aggregate.
• Service: Domain logic that doesn't belong to a specific entity.

Domain Events

DomainEvent OrderPlaced {
  - OrderId orderId
  Date timestamp
}