Within DDD, the idea is to allocate all logic (as much as feasible) to the entity POJOs. This often includes logic of the following categories: accessing state (setters, getters, navigation and change of object graph), validating the state, calculation of derived attributes (calculating order sum of an order) and event processing (action-logic triggered by changes to the state of an entity, such as producing a shipment note when the order state is changed to “ready-for-shipment”). With large systems, there are usually context-specific (e.g. use-case-specific) needs that influence what methods we add to the domain classes. This creates problems over time when there are a lot of context-specific change requests that require new versions of a shared domain model implementation. With dynamic languages it is straightforward to separate these concerns without sacrificing the sought-after programming model of "intelligent pojos". There is also a new architecture (DCI) that take the reasoning further, towards a formal architecture for separation of concerns that is driven by the same core problem: how to get the fruit of DDD without the downside of a fragile domain model? This presentation illustrates pragmatic CDI with the power of a dynamic language (Groovy).

3. My goal with this talk is to… … make your brain boil of inspiration!

5. DDD works well for this…

6. But less well for this… … which is quite common in midsize- to large systems

7. Because you either end up with this…

8. … or this….

9. What if…. … use-case logic could be ATTACHED to domain objects when needed but still OWNED by the application modul?

10. Like this….

11. Compile-time…

12. Deploy-time…

13. Runtime view…. … of an interaction within the ProduceQuarterlyForecast use-case…

14. Runtime view…. … of an interaction within the SendSignedOrdersToSupplier use-case…

15. Taking a look at the role implementation…. public class Article { List<OrderItem> ordered ; PriceList pricelist ; public BigDecimal calcNextQuaterSales() { BigDecimal qSales = … ordered .findAll {OrderItem item -> item.deliveryDate > Calendar.nextQuaterStart && item.deliveryDate < Calendar.nextQuaterEnd}.each {OrderItem item -> qSales += item.amount * pricelist .meanPriceBetweenDates (Calendar.nextQuaterStart, Calendar.nextQuaterEnd) } return qSales } }

18. Groovy Mixin Simple Sample Context: CalculateNetPriceContext Data: a BigDecimal Interaction: netPrice on Role PriceRole

19. The code – Define the Role (the mixin) class PriceRole { BigDecimal getNetPrice() { return this * 0.8 } } class CalculateNetPriceContext { def priceRole CalculateNetPriceContext(BigDecimal amount) { amount.metaClass.mixin(PriceRole) priceRole = amount } BigDecimal executeContext() { return priceRole.netPrice } } println new CalculateNetPriceContext(100.00).executeContext()

20. The code – Context assigns role to data class PriceRole { BigDecimal getNetPrice() { return this * 0.8 } } class CalculateNetPriceContext { def priceRole CalculateNetPriceContext(BigDecimal amount) { amount.metaClass.mixin(PriceRole) priceRole = amount } BigDecimal executeContext() { return priceRole.netPrice } } println new CalculateNetPriceContext(100.00).executeContext()

21. The code – method to execute interaction class PriceRole { BigDecimal getNetPrice() { return this * 0.8 } } class CalculateNetPriceContext { def priceRole CalculateNetPriceContext(BigDecimal amount) { amount.metaClass.mixin(PriceRole) priceRole = amount } BigDecimal executeContext() { return priceRole.netPrice } } println new CalculateNetPriceContext(100.00).executeContext()

22. The code – ask the context to conduct the interaction class PriceRole { BigDecimal getNetPrice() { return this * 0.8 } } class CalculateNetPriceContext { def priceRole CalculateNetPriceContext(BigDecimal amount) { amount.metaClass.mixin(PriceRole) priceRole = amount } BigDecimal executeContext() { return priceRole.netPrice } } println new CalculateNetPriceContext(100.00).executeContext()

23. Let ’ s revisit the BIG system….

24. Clean dependency graph!

30. Thanks for listening! Questions? ?