Refactor: 멘토 슬롯-예약 1:N 관계로 변경 (#158)

* Refactor: 슬롯:예약 1:N 관계로 변경

* Refactor: 슬롯 목록 조회 시 활성화된 예약 ID 함께 반환

* Refactor: Member객체 아닌 memberId로 조회

* Refactor: 멘티의 기존 예약 시간 중복 확인

Author: sso0om

back/src/main/java/com/back/domain/mentoring/reservation/entity/Reservation.java

@@ -37,7 +37,7 @@ public class Reservation extends BaseEntity {
     @JoinColumn(name = "mentee_id", nullable = false)
     private Mentee mentee;
 
-    @OneToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "mentor_slot_id", nullable = false)
     private MentorSlot mentorSlot;
 
@@ -63,13 +63,6 @@ public Reservation(Mentoring mentoring, Mentee mentee, MentorSlot mentorSlot, St
 
     private void updateStatus(ReservationStatus status) {
         this.status = status;
-
-        // 양방향 동기화
-        if (status == ReservationStatus.CANCELED || status == ReservationStatus.REJECTED) {
-            mentorSlot.removeReservation();
-        } else {
-            mentorSlot.updateStatus();
-        }
     }
 
     public boolean isMentor(Mentor mentor) {

back/src/main/java/com/back/domain/mentoring/reservation/error/ReservationErrorCode.java

@@ -30,7 +30,8 @@ public enum ReservationErrorCode implements ErrorCode {
     NOT_AVAILABLE_SLOT("409-1", "이미 예약이 완료된 시간대입니다."),
     ALREADY_RESERVED_SLOT("409-2", "이미 예약한 시간대입니다. 예약 목록을 확인해 주세요."),
     CONCURRENT_RESERVATION_CONFLICT("409-3", "다른 사용자가 먼저 예약했습니다. 새로고침 후 다시 시도해 주세요."),
-    CONCURRENT_APPROVAL_CONFLICT("409-4", "이미 수락한 예약입니다.");
+    CONCURRENT_APPROVAL_CONFLICT("409-4", "이미 수락한 예약입니다."),
+    OVERLAPPING_TIME("409-5", "이미 해당 시간에 다른 예약이 있습니다. 예약 목록을 확인해 주세요.");
 
     private final String code;
     private final String message;

back/src/main/java/com/back/domain/mentoring/reservation/repository/ReservationRepository.java

@@ -9,6 +9,7 @@
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
 
+import java.time.LocalDateTime;
 import java.util.List;
 import java.util.Optional;
 
@@ -20,22 +21,22 @@ public interface ReservationRepository extends JpaRepository<Reservation, Long>
         SELECT r
         FROM Reservation r
         WHERE r.id = :reservationId
-        AND (r.mentee.member = :member
-            OR r.mentor.member = :member)
+        AND (r.mentee.member.id = :memberId
+            OR r.mentor.member.id = :memberId)
         """)
     Optional<Reservation> findByIdAndMember(
         @Param("reservationId") Long reservationId,
-        @Param("member") Member member
+        @Param("memberId") Long memberId
     );
 
     @Query("""
         SELECT r
         FROM Reservation r
-        WHERE r.mentor.member = :member
+        WHERE r.mentor.member.id = :memberId
         ORDER BY r.mentorSlot.startDateTime DESC
         """)
     Page<Reservation> findAllByMentorMember(
-        @Param("member") Member member,
+        @Param("memberId") Long memberId,
         Pageable pageable
     );
 
@@ -58,4 +59,21 @@ Page<Reservation> findAllByMenteeMember(
      * - 취소/거절된 예약도 히스토리로 보존
      */
     boolean existsByMentorSlotId(Long slotId);
+
+    @Query("""
+        SELECT CASE WHEN COUNT(r) > 0
+            THEN TRUE
+            ELSE FALSE
+            END
+        FROM Reservation r
+        WHERE r.mentee.id = :menteeId
+        AND r.status NOT IN ('REJECTED', 'CANCELED')
+        AND r.mentorSlot.startDateTime < :end
+        AND r.mentorSlot.endDateTime > :start
+        """)
+    boolean existsOverlappingTimeForMentee(
+        @Param("menteeId") Long menteeId,
+        @Param("start") LocalDateTime start,
+        @Param("end") LocalDateTime end
+    );
 }

back/src/main/java/com/back/domain/mentoring/reservation/service/ReservationService.java

@@ -12,6 +12,7 @@
 import com.back.domain.mentoring.reservation.entity.Reservation;
 import com.back.domain.mentoring.reservation.error.ReservationErrorCode;
 import com.back.domain.mentoring.reservation.repository.ReservationRepository;
+import com.back.domain.mentoring.slot.constant.MentorSlotStatus;
 import com.back.domain.mentoring.slot.entity.MentorSlot;
 import com.back.domain.mentoring.slot.service.DateTimeValidator;
 import com.back.global.exception.ServiceException;
@@ -40,7 +41,7 @@ public Page<ReservationDto> getReservations(Member member, int page, int size) {
         Page<Reservation> reservations;
 
         if (member.getRole() == Member.Role.MENTOR) {
-            reservations = reservationRepository.findAllByMentorMember(member, pageable);
+            reservations = reservationRepository.findAllByMentorMember(member.getId(), pageable);
         } else {
             reservations = reservationRepository.findAllByMenteeMember(member, pageable);
         }
@@ -49,7 +50,7 @@ public Page<ReservationDto> getReservations(Member member, int page, int size) {
 
     @Transactional(readOnly = true)
     public ReservationResponse getReservation(Member member, Long reservationId) {
-        Reservation reservation = reservationRepository.findByIdAndMember(reservationId, member)
+        Reservation reservation = reservationRepository.findByIdAndMember(reservationId, member.getId())
             .orElseThrow(() -> new ServiceException(ReservationErrorCode.RESERVATION_NOT_ACCESSIBLE));
 
         return ReservationResponse.from(reservation);
@@ -61,21 +62,20 @@ public ReservationResponse createReservation(Mentee mentee, ReservationRequest r
             Mentoring mentoring = mentoringStorage.findMentoring(reqDto.mentoringId());
             MentorSlot mentorSlot = mentoringStorage.findMentorSlot(reqDto.mentorSlotId());
 
-            validateMentorSlotStatus(mentorSlot, mentee);
             DateTimeValidator.validateStartTimeNotInPast(mentorSlot.getStartDateTime());
+            validateMentorSlotStatus(mentorSlot, mentee);
+            validateOverlappingTimeForMentee(mentee, mentorSlot);
 
             Reservation reservation = Reservation.builder()
                 .mentoring(mentoring)
                 .mentee(mentee)
                 .mentorSlot(mentorSlot)
                 .preQuestion(reqDto.preQuestion())
                 .build();
-
-            mentorSlot.setReservation(reservation);
-            // flush 필요...?
-
             reservationRepository.save(reservation);
 
+            mentorSlot.updateStatus(MentorSlotStatus.PENDING);
+
             return ReservationResponse.from(reservation);
         } catch (OptimisticLockException e) {
             throw new ServiceException(ReservationErrorCode.CONCURRENT_RESERVATION_CONFLICT);
@@ -88,6 +88,7 @@ public ReservationResponse approveReservation(Mentor mentor, Long reservationId)
             Reservation reservation = mentoringStorage.findReservation(reservationId);
 
             reservation.approve(mentor);
+            reservation.getMentorSlot().updateStatus(MentorSlotStatus.APPROVED);
 
             // 세션
 
@@ -101,13 +102,17 @@ public ReservationResponse approveReservation(Mentor mentor, Long reservationId)
     public ReservationResponse rejectReservation(Mentor mentor, Long reservationId) {
         Reservation reservation = mentoringStorage.findReservation(reservationId);
         reservation.reject(mentor);
+        reservation.getMentorSlot().updateStatus(MentorSlotStatus.AVAILABLE);
+
         return ReservationResponse.from(reservation);
     }
 
     @Transactional
     public ReservationResponse cancelReservation(Member member, Long reservationId) {
         Reservation reservation = mentoringStorage.findReservation(reservationId);
         reservation.cancel(member);
+        reservation.getMentorSlot().updateStatus(MentorSlotStatus.AVAILABLE);
+
         return ReservationResponse.from(reservation);
     }
 
@@ -127,4 +132,13 @@ private void validateMentorSlotStatus(MentorSlot mentorSlot, Mentee mentee) {
             throw new ServiceException(ReservationErrorCode.NOT_AVAILABLE_SLOT);
         }
     }
+
+    private void validateOverlappingTimeForMentee(Mentee mentee, MentorSlot mentorSlot) {
+        boolean isOverlapping = reservationRepository
+            .existsOverlappingTimeForMentee(mentee.getId(), mentorSlot.getStartDateTime(), mentorSlot.getEndDateTime());
+
+        if (isOverlapping) {
+            throw new ServiceException(ReservationErrorCode.OVERLAPPING_TIME);
+        }
+    }
 }

back/src/main/java/com/back/domain/mentoring/slot/dto/response/MentorSlotDto.java

@@ -1,7 +1,6 @@
 package com.back.domain.mentoring.slot.dto.response;
 
 import com.back.domain.mentoring.slot.constant.MentorSlotStatus;
-import com.back.domain.mentoring.slot.entity.MentorSlot;
 import io.swagger.v3.oas.annotations.media.Schema;
 
 import java.time.LocalDateTime;
@@ -16,15 +15,8 @@ public record MentorSlotDto(
     @Schema(description = "종료 일시")
     LocalDateTime endDateTime,
     @Schema(description = "멘토 슬롯 상태")
-    MentorSlotStatus mentorSlotStatus
+    MentorSlotStatus mentorSlotStatus,
+    @Schema(description = "활성화된 예약 ID")
+    Long reservationId
 ) {
-    public static MentorSlotDto from(MentorSlot mentorSlot) {
-        return new MentorSlotDto(
-            mentorSlot.getId(),
-            mentorSlot.getMentor().getId(),
-            mentorSlot.getStartDateTime(),
-            mentorSlot.getEndDateTime(),
-            mentorSlot.getStatus()
-        );
-    }
 }

back/src/main/java/com/back/domain/mentoring/slot/entity/MentorSlot.java

@@ -1,7 +1,6 @@
 package com.back.domain.mentoring.slot.entity;
 
 import com.back.domain.member.mentor.entity.Mentor;
-import com.back.domain.mentoring.reservation.entity.Reservation;
 import com.back.domain.mentoring.slot.constant.MentorSlotStatus;
 import com.back.global.jpa.BaseEntity;
 import jakarta.persistence.*;
@@ -25,9 +24,6 @@ public class MentorSlot extends BaseEntity {
     @Column(nullable = false)
     private LocalDateTime endDateTime;
 
-    @OneToOne(mappedBy = "mentorSlot")
-    private Reservation reservation;
-
     @Enumerated(EnumType.STRING)
     @Column(nullable = false)
     private MentorSlotStatus status;
@@ -48,41 +44,8 @@ public void updateTime(LocalDateTime startDateTime, LocalDateTime endDateTime) {
         this.endDateTime = endDateTime;
     }
 
-    // =========================
-    // TODO - 현재 상태
-    // 1. reservation 필드에는 활성 예약(PENDING, APPROVED)만 세팅
-    // 2. 취소/거절 예약은 DB에 남기고 reservation 필드에는 연결하지 않음
-    // 3. 슬롯 재생성 불필요, 상태 기반 isAvailable() 로 새 예약 가능 판단
-    //
-    // TODO - 추후 변경
-    // 1. 1:N 구조로 리팩토링
-    //    - MentorSlot에 여러 Reservation 연결 가능
-    //    - 모든 예약 기록(히스토리) 보존
-    // 2. 상태 기반 필터링 유지: 활성 예약만 계산 시 사용
-    // 3. 이벤트 소싱/분석 등 확장 가능하도록 구조 개선
-    // =========================
-
-    public void updateStatus() {
-        if (reservation == null) {
-            this.status =  MentorSlotStatus.AVAILABLE;
-        } else {
-            this.status = switch (reservation.getStatus()) {
-                case PENDING -> MentorSlotStatus.PENDING;
-                case APPROVED -> MentorSlotStatus.APPROVED;
-                case COMPLETED -> MentorSlotStatus.COMPLETED;
-                case REJECTED, CANCELED -> MentorSlotStatus.AVAILABLE;
-            };
-        }
-    }
-
-    public void setReservation(Reservation reservation) {
-        this.reservation = reservation;
-        updateStatus();
-    }
-
-    public void removeReservation() {
-        this.reservation = null;
-        this.status = MentorSlotStatus.AVAILABLE;
+    public void updateStatus(MentorSlotStatus status) {
+        this.status = status;
     }
 
     /**
@@ -91,7 +54,7 @@ public void removeReservation() {
      * - 예약이 취소/거절된 경우 true
      */
     public boolean isAvailable() {
-        return reservation == null;
+        return status == MentorSlotStatus.AVAILABLE;
     }
 
     public boolean isOwnerBy(Mentor mentor) {

back/src/main/java/com/back/domain/mentoring/slot/repository/MentorSlotRepository.java

@@ -1,5 +1,6 @@
 package com.back.domain.mentoring.slot.repository;
 
+import com.back.domain.mentoring.slot.dto.response.MentorSlotDto;
 import com.back.domain.mentoring.slot.entity.MentorSlot;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
@@ -17,35 +18,51 @@ public interface MentorSlotRepository extends JpaRepository<MentorSlot, Long> {
     void deleteAllByMentorId(Long mentorId);
 
     @Query("""
-        SELECT ms
+        SELECT new com.back.domain.mentoring.slot.dto.response.MentorSlotDto(
+            ms.id,
+            ms.mentor.id,
+            ms.startDateTime,
+            ms.endDateTime,
+            ms.status,
+            r.id
+        )
         FROM MentorSlot ms
+        LEFT JOIN Reservation r
+            ON ms.id = r.mentorSlot.id
+            AND r.status IN ('PENDING', 'APPROVED', 'COMPLETED')
         WHERE ms.mentor.id = :mentorId
         AND ms.startDateTime < :end
         AND ms.endDateTime >= :start
         ORDER BY ms.startDateTime ASC
         """)
-    List<MentorSlot> findMySlots(
+    List<MentorSlotDto> findMySlots(
         @Param("mentorId") Long mentorId,
         @Param("start") LocalDateTime start,
         @Param("end") LocalDateTime end
     );
 
     @Query("""
-        SELECT ms
+        SELECT new com.back.domain.mentoring.slot.dto.response.MentorSlotDto(
+                ms.id,
+                ms.mentor.id,
+                ms.startDateTime,
+                ms.endDateTime,
+                ms.status,
+                NULL
+        )
         FROM MentorSlot ms
         WHERE ms.mentor.id = :mentorId
         AND ms.status = 'AVAILABLE'
         AND ms.startDateTime < :end
         AND ms.endDateTime >= :start
         ORDER BY ms.startDateTime ASC
         """)
-    List<MentorSlot> findAvailableSlots(
+    List<MentorSlotDto> findAvailableSlots(
         @Param("mentorId") Long mentorId,
         @Param("start") LocalDateTime start,
         @Param("end") LocalDateTime end
     );
 
-    // TODO: 현재는 시간 겹침만 체크, 추후 1:N 구조 시 활성 예약 기준으로 변경
     @Query("""
         SELECT CASE WHEN COUNT(ms) > 0
                 THEN TRUE

back/src/main/java/com/back/domain/mentoring/slot/service/MentorSlotService.java

@@ -33,22 +33,14 @@ public class MentorSlotService {
     public List<MentorSlotDto> getMyMentorSlots(Mentor mentor, LocalDateTime startDate, LocalDateTime endDate) {
         DateTimeValidator.validateTime(startDate, endDate);
 
-        List<MentorSlot> availableSlots = mentorSlotRepository.findMySlots(mentor.getId(), startDate, endDate);
-
-        return availableSlots.stream()
-            .map(MentorSlotDto::from)
-            .toList();
+        return mentorSlotRepository.findMySlots(mentor.getId(), startDate, endDate);
     }
 
     @Transactional(readOnly = true)
     public List<MentorSlotDto> getAvailableMentorSlots(Long mentorId, LocalDateTime startDate, LocalDateTime endDate) {
         DateTimeValidator.validateTime(startDate, endDate);
 
-        List<MentorSlot> availableSlots = mentorSlotRepository.findAvailableSlots(mentorId, startDate, endDate);
-
-        return availableSlots.stream()
-            .map(MentorSlotDto::from)
-            .toList();
+        return mentorSlotRepository.findAvailableSlots(mentorId, startDate, endDate);
     }
 
     @Transactional(readOnly = true)

back/src/test/java/com/back/domain/mentoring/reservation/controller/ReservationControllerTest.java

@@ -2,7 +2,6 @@
 
 import com.back.domain.member.member.entity.Member;
 import com.back.domain.member.member.service.AuthTokenService;
-import com.back.domain.member.mentee.entity.Mentee;
 import com.back.domain.member.mentor.entity.Mentor;
 import com.back.domain.mentoring.mentoring.entity.Mentoring;
 import com.back.domain.mentoring.reservation.entity.Reservation;
@@ -49,7 +48,6 @@ class ReservationControllerTest {
     private static final String RESERVATION_URL = "/reservations";
 
     private Mentor mentor;
-    private Mentee mentee;
     private Mentoring mentoring;
     private MentorSlot mentorSlot;
     private String menteeToken;
@@ -62,7 +60,7 @@ void setUp() {
 
         // Mentee
         Member menteeMember = memberFixture.createMenteeMember();
-        mentee = memberFixture.createMentee(menteeMember);
+        memberFixture.createMentee(menteeMember);
         menteeToken = authTokenService.genAccessToken(menteeMember);
 
         // Mentoring, MentorSlot