Skip to main content

Override a read use case

Goal: change the behaviour of one read — here, list events 12 per page sorted by newest instead of the platform's 6-by-start-date — without touching the controller, the store or any other use case.

  • Seam: GetEventsUseCase<T extends EventSummaryDto> (single-method use-case interface).
  • City files: one @Service.
  • Applies to: both topologies.

Recipe​

Declare a @Service implementing the interface anywhere under com.modelcity.<vertical>. DefaultGetEventsUseCase backs off automatically.

// com.modelcity.leisure.events.usecase.MyGetEventsUseCase
@Service
@RequiredArgsConstructor
public class MyGetEventsUseCase implements GetEventsUseCase<EventSummaryDto> {

    private static final int PAGE_SIZE = 12;   // was 6

    private final EventStore<? extends EventView, EventRequestDto> eventStore;

    @Override
    @Cacheable(cacheNames = CacheNames.EVENTS, key = "#locale + '-' + #type + '-' + #paid + '-' + #page")
    @Transactional(readOnly = true)
    public Page<EventSummaryDto> execute(EventType type, Boolean paid, int page, String locale) {
        PageRequest pageable = PageRequest.of(page, PAGE_SIZE, Sort.by("startsAt").descending());
        return eventStore.search(type, paid, LocalDateTime.now(), pageable)
                .map(e -> EventSummaryDto.from(e, locale));
    }
}

Notes​

  • Re-declare @Cacheable / @Transactional. They live on DefaultGetEventsUseCase, and annotations are not inherited across separate implementations. Omit @Cacheable on purpose to disable caching for this use case while the rest keep theirs.
  • Reuse the same ports and factories (EventStore, EventSummaryDto.from) — you are changing policy, not re-plumbing persistence.
  • To also return extra fields, this becomes an expose-a-new-field job (subtype the DTO and bind the controller).
  • Overriding is whole-method: implement the smallest use case that isolates your change, not a coarse one, so you inherit platform fixes to the others.

Verify​

npm-free: start the app and curl "/events?page=0" — 12 items, newest first. A non-overridden read (e.g. GET /city-places) is unchanged, and the startup log shows Model City default 'defaultGetEventsUseCase' … disabled: seam GetEventsUseCase is covered by bean 'myGetEventsUseCase'.