refactor: TrackingSession 조회 시 fetch join 적용하여 N+1 쿼리 제거

closes #275

Author: howooyeon

src/main/java/com/semosan/api/domain/tracking/dto/response/TrackingSessionResponse.java

@@ -29,13 +29,14 @@ public static TrackingSessionResponse from(TrackingSession session) {
     }
 
     public static TrackingSessionResponse from(TrackingSession session, Long hikingRecordId) {
+        var course = session.getCourse();
         return new TrackingSessionResponse(
                 session.getId(),
                 session.getUser().getId(),
                 session.getMountain().getId(),
                 session.getMountain().getName(),
-                session.getCourse() != null ? session.getCourse().getId() : null,
-                session.getCourse() != null ? session.getCourse().getName() : null,
+                course != null ? course.getId() : null,
+                course != null ? course.getName() : null,
                 session.getIsFreeRecording(),
                 session.getStatus(),
                 session.getStartedAt(),

src/main/java/com/semosan/api/domain/tracking/repository/TrackingSessionRepository.java

@@ -22,6 +22,29 @@ Optional<TrackingSession> findFirstByUser_IdAndStatusInOrderByStartedAtDesc(
             Collection<TrackingSessionStatus> statuses
     );
 
+    @Query("""
+            SELECT ts FROM TrackingSession ts
+            JOIN FETCH ts.user
+            JOIN FETCH ts.mountain
+            LEFT JOIN FETCH ts.course
+            WHERE ts.id = :id
+            """)
+    Optional<TrackingSession> findByIdWithRelations(@Param("id") Long id);
+
+    @Query("""
+            SELECT ts FROM TrackingSession ts
+            JOIN FETCH ts.user
+            JOIN FETCH ts.mountain
+            LEFT JOIN FETCH ts.course
+            WHERE ts.user.id = :userId AND ts.status IN :statuses
+            ORDER BY ts.startedAt DESC
+            LIMIT 1
+            """)
+    Optional<TrackingSession> findFirstActiveWithRelations(
+            @Param("userId") Long userId,
+            @Param("statuses") Collection<TrackingSessionStatus> statuses
+    );
+
     /**
      * 24h 자동 만료 스케줄러용.
      * 활성 상태(IN_PROGRESS/PAUSED) 이면서 마지막 업데이트가 cutoff 이전인 세션을 찾는다.

src/main/java/com/semosan/api/domain/tracking/service/TrackingSessionService.java

@@ -82,7 +82,7 @@ public TrackingSessionResponse create(Long userId, CreateTrackingSessionRequest
 
     public Optional<TrackingSessionResponse> getActive(Long userId) {
         return trackingSessionRepository
-                .findFirstByUser_IdAndStatusInOrderByStartedAtDesc(userId, TrackingSessionStatus.ACTIVE_STATES)
+                .findFirstActiveWithRelations(userId, TrackingSessionStatus.ACTIVE_STATES)
                 .map(TrackingSessionResponse::from);
     }
 
@@ -158,7 +158,7 @@ public TrackingSessionResponse abandon(Long userId, Long sessionId) {
     }
 
     private TrackingSession findOwnedSession(Long userId, Long sessionId) {
-        TrackingSession session = trackingSessionRepository.findById(sessionId)
+        TrackingSession session = trackingSessionRepository.findByIdWithRelations(sessionId)
                 .orElseThrow(() -> new GeneralException(ErrorStatus.TRACKING_SESSION_NOT_FOUND));
         if (!session.isOwnedBy(userId)) {
             throw new GeneralException(ErrorStatus.TRACKING_SESSION_FORBIDDEN);