순환 의존을 이벤트로 끊은 이야기 — Aggregate 간 통신 패턴

@Service
@RequiredArgsConstructor
public class CreatePostingUseCase {
    private final PostingService postingService;
    private final StepService stepService;  // Step Aggregate에 직접 의존
 
    @Transactional
    public PostingWithDetailDto execute(final CreatePostingCommand command) {
        final PostingWithDetailDto posting = postingService.create(command);
        stepService.configureDefaultSteps(posting.getId(), defaultStepCommands);  // 직접 호출
        return posting;
    }
}

// PostingUseCase → StepService 의존 (공고 생성 시 전형 생성)
// StepUseCase → PostingService 의존 (전형 삭제 시 공고 상태 확인)
// → 순환 의존!

// Posting UseCase — Step을 전혀 모른다
@Service
@RequiredArgsConstructor
public class CreatePostingUseCase {
    private final PostingService postingService;
    private final ApplicationEventPublisher eventPublisher;
 
    @Transactional
    public PostingWithDetailDto execute(final CreatePostingCommand command) {
        final PostingWithDetailDto posting = postingService.create(command);
        eventPublisher.publishEvent(new PostingCreatedEvent(posting));
        return posting;
    }
}

// Step Aggregate가 Posting 이벤트에 반응
@Slf4j
@RequiredArgsConstructor
@Component
public class StepEventListener {
    private final StepService stepService;
    private final DeleteStepUseCase deleteStepUseCase;
    private final AtsProps atsProps;
 
    @Async
    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
    public void createDefaultSteps(final PostingCreatedEvent event) {
        try {
            final PostingWithDetailDto posting = event.getPosting();
            final List<CreateStepCommand> commands = atsProps.getDefaultStepNames().stream()
                .map(stepName -> CreateStepCommand.builder()
                    .name(stepName)
                    .build())
                .toList();
            stepService.configureDefaultSteps(posting.getId(), commands);
        } catch (final Exception e) {
            log.error("공고 생성 시 기본 전형 생성 에러", e);
        }
    }
 
    @Async
    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
    public void deleteSteps(final PostingDeletedEvent event) {
        try {
            deleteStepUseCase.deleteSteps(event.getPosting().getId());
        } catch (final Exception e) {
            log.error("공고 삭제 시 전형 삭제 에러", e);
        }
    }
}

// 결제 완료 이벤트 — 장바구니 아이템 ID만 담는다
public record PaymentCompletedEvent(List<Long> cartItemIds) {
    public static PaymentCompletedEvent from(final Order order) {
        return new PaymentCompletedEvent(order.getCartItemIds());
    }
}

// Cart Aggregate의 리스너
@Slf4j
@RequiredArgsConstructor
@Component
public class CartEventListener {
 
    private final UpdateCartItemOrderedUseCase updateCartItemOrderedUseCase;
 
    @Async
    @Transactional(propagation = Propagation.REQUIRES_NEW)
    @TransactionalEventListener(phase = TransactionPhase.AFTER_COMMIT)
    public void updateApplicationDuplicated(final PaymentCompletedEvent event) {
        log.info("결제 성공 후 장바구니 항목 삭제");
        try {
            final List<Long> cartItemIds = event.cartItemIds();
            updateCartItemOrderedUseCase.updateCartItem(cartItemIds);
        } catch (final Exception e) {
            log.error("결제 성공 후 장바구니 항목 삭제 실패 : {}", e.getMessage(), e);
        }
    }
}