도메인 주도 설계의 사실과 오해 2부 (3) 모델의 경계를 긋고, 핵심에 집중하라

public class Ticket { public Money price() { ... } public Order buy() { ... } public Seat position() { ... } public boolean isStanding() { ... } public void deliver() { ... } public void print() { ... } }

public class Ticket { public Money price() { ... } public Order buy() { ... } public Seat position() { ... } public boolean isStanding() { ... } }

public class Ticket { public Seat position() { ... } public boolean isStanding() { ... } public void deliver() { ... } }

public class Ticket { public void print() { ... } }

public abstract class RatePlan extends AggregateRoot<RatePlan, Long> { public Money calculateFee(Collection<CallRecord[]> calls) { return calls.stream() .map(call -> this.calculateCallFee(call[0], call[1])) .reduce(Money.ZERO, Money::plus); } protected abstract Money calculateCallFee(CallRecord started, CallRecord completed); }

public class RegularRatePlan extends RatePlan { private Money amount; // 단위 금액 private Duration duration; // 단위 시간 @Override protected Money calculateCallFee(CallRecord started, CallRecord completed) { return amount.times( TimeInterval.of(started.getOccurredTime(), completed.getOccurredTime()) .duration().dividedBy(duration)); } }

public class NightRatePlan extends RatePlan { private static final TimeInterval<LocalTime> NIGHT = TimeInterval.of(LocalTime.of(22, 0), LocalTime.of(6, 0)); private Money nightAmount; // 심야 단위 금액 private Money dayAmount; // 주간 단위 금액 private Duration duration; // 단위 시간 @Override protected Money calculateCallFee(CallRecord started, CallRecord completed) { Duration callDuration = TimeInterval.of( started.getOccurredTime(), completed.getOccurredTime()).duration(); if (NIGHT.include(started.getOccurredTime().toLocalTime())) { return nightAmount.times(callDuration.dividedBy(duration)); } return dayAmount.times(callDuration.dividedBy(duration)); } }

@Service @AllArgsConstructor public class PhoneBillService { private ContractRepository contractRepository; private RatePlanRepository ratePlanRepository; private CallRecordRepository callRecordRepository; private PhoneBillRepository phoneBillRepository; @Transactional public void calculate(Long contractId) { Contract contract = contractRepository.findById(contractId) .orElseThrow(IllegalArgumentException::new); RatePlan ratePlan = ratePlanRepository.findById(contract.getRatePlanId()) .orElseThrow(IllegalArgumentException::new); Collection<CallRecord[]> callRecords = callRecordRepository.findCallRecordsToBill(contract.getPhoneNumber()); PhoneBill bill = new PhoneBill(contractId, contract.getPhone(), ratePlan.calculateFee(callRecords)); phoneBillRepository.save(bill); } }

org.eternity.phone +-- contract/ # 계약관리팀 | +-- domain/ # Contract, Phone, RatePlan, PhoneBill | +-- service/ # PhoneBillService +-- tracking/ # 통화관리팀 | +-- domain/ # CallRecord, CallSession, CallPhase, CallStatus | +-- service/ # CallService

// contract/domain/RatePlan.java import org.eternity.phone.tracking.domain.CallRecord; // 바운디드 컨텍스트 침범! protected abstract Money calculateCallFee(CallRecord started, CallRecord completed);

// contract/domain/Call.java public record Call(String phoneNumber, TimeInterval<LocalDateTime> period) { public Duration duration() { return period.duration(); } public LocalTime startTime() { return period.getStart().toLocalTime(); } }

// tracking/service/CallRecordFacade.java @Component @AllArgsConstructor public class CallRecordFacade { private CallRecordRepository callRecordRepository; public Collection<CallRecordPair> getCallRecords(String phoneNumber) { Collection<CallRecord[]> result = callRecordRepository.findCallRecordsToBill(phoneNumber); return result.stream() .map(call -> new CallRecordPair(call[0], call[1])) .toList(); } }

// contract/domain/CallTranslator.java public interface CallTranslator { Collection<Call> translate(String phoneNumber); }

// contract/service/CallRecordToCallTranslator.java @Component @AllArgsConstructor public class CallRecordToCallTranslator implements CallTranslator { private CallRecordRepository callRecordRepository; public Collection<Call> translate(String phoneNumber) { Collection<CallRecord[]> callRecords = callRecordRepository.findCallRecordsToBill(phoneNumber); return callRecords.stream() .map(pair -> new Call( pair[0].getCallingNumber(), TimeInterval.of(pair[0].getOccurredTime(), pair[1].getOccurredTime()))) .collect(Collectors.toUnmodifiableSet()); } }

// 변경 전 (02-integrity-error) protected abstract Money calculateCallFee(CallRecord started, CallRecord completed); // 변경 후 (03-bounded-context) protected abstract Money calculateCallFee(Call call);

protected Money calculateCallFee(Call call) { return amount.times(call.duration().dividedBy(duration)); }

contract/ enrollment/ → 지원 서브도메인 (Contract, Phone) rateplan/ → 코어 도메인 (RatePlan, RegularRatePlan, NightRatePlan) billing/ → 지원 서브도메인 (PhoneBill, Call, CallTranslator, PhoneBillService)

public abstract class RatePlan extends AggregateRoot<RatePlan, Long> { public Money calculateFee(Collection<Call> calls) { Money fee = calls.stream() .map(call -> this.calculateCallFee(call)) .reduce(Money.ZERO, Money::plus); return afterCalculated(fee); // 부가 정책 적용 훅 } protected Money afterCalculated(Money fee) { return fee; } // 기본: 아무것도 안 함 protected abstract Money calculateCallFee(Call call); }

public class RegularRateAndTaxablePlan extends RegularRatePlan { private double taxRate; @Override protected Money afterCalculated(Money fee) { return super.afterCalculated(fee).plus(fee.times(taxRate)); } }

RatePlan (abstract) +-- RegularRatePlan | +-- RegularRateAndTaxablePlan (세금만) | | +-- RegularRateAndTaxableAndDiscountablePlan (세금 먼저 + 할인) | +-- RegularRateAndDiscountablePlan (할인만) | +-- RegularRateAndDiscountableAndTaxablePlan (할인 먼저 + 세금) +-- NightRatePlan +-- NightRateAndTaxablePlan (세금만) | +-- NightRateAndTaxableAndDiscountablePlan (세금 먼저 + 할인) +-- NightRateAndDiscountablePlan (할인만) +-- NightRateAndDiscountableAndTaxablePlan (할인 먼저 + 세금)

public abstract class AdditionalRatePlan { private AdditionalRatePlan next; // 체인 연결 public Money calculate(Money fee) { if (next == null) { return apply(fee); } return next.calculate(apply(fee)); // 현재 적용 후 다음으로 전달 } protected abstract Money apply(Money fee); }

public class TaxableRatePlan extends AdditionalRatePlan { private double taxRate; @Override protected Money apply(Money fee) { return fee.plus(fee.times(taxRate)); } } public class DiscountableRatePlan extends AdditionalRatePlan { private Money discountAmount; @Override protected Money apply(Money fee) { return fee.minus(discountAmount); } }

public abstract class RatePlan { private AdditionalRatePlan additionalRatePlan; // 부가 정책 체인 public Money calculateFee(Collection<Call> calls) { Money fee = calls.stream() .map(call -> this.calculateCallFee(call)) .reduce(Money.ZERO, Money::plus); if (additionalRatePlan != null) { return additionalRatePlan.calculate(fee); // 부가 정책 적용 } return fee; } protected abstract Money calculateCallFee(Call call); }

// 일반 요금제 + 할인 + 세금 (체이닝) RegularRatePlan plan = new RegularRatePlan( Money.won(10), Duration.ofSeconds(10), new DiscountableRatePlan(Money.won(1), new TaxableRatePlan(0.1))); Money fee = plan.calculateFee(calls);