fix:conflict 해결

Author: iamjieunkim

src/main/java/com/threestar/trainus/domain/lesson/teacher/repository/LessonRepository.java

@@ -7,13 +7,16 @@
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.data.jpa.repository.Lock;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
 
 import com.threestar.trainus.domain.lesson.teacher.entity.Category;
 import com.threestar.trainus.domain.lesson.teacher.entity.Lesson;
 import com.threestar.trainus.domain.lesson.teacher.entity.LessonStatus;
 
+import jakarta.persistence.LockModeType;
+
 public interface LessonRepository extends JpaRepository<Lesson, Long> {
 	//삭제되지 않은 레슨만 조회
 	Optional<Lesson> findByIdAndDeletedAtIsNull(Long lessonId);
@@ -107,4 +110,8 @@ WHERE l.status IN (
 		AND l.deletedAt IS NULL
 		""")
 	List<Lesson> findLessonsToComplete(@Param("now") LocalDateTime now);
+
+	@Lock(LockModeType.PESSIMISTIC_WRITE) // 비관적 락 적용
+	@Query("SELECT l FROM Lesson l WHERE l.id = :lessonId")
+	Optional<Lesson> findByIdWithLock(@Param("lessonId") Long lessonId);
 }

src/main/java/com/threestar/trainus/domain/lesson/teacher/service/AdminLessonService.java

@@ -458,6 +458,12 @@ public Lesson findLessonById(Long lessonId) {
 			.orElseThrow(() -> new BusinessException(ErrorCode.LESSON_NOT_FOUND));
 	}
 
+	// develop 브랜치에서 추가된 메서드 - Lock 기능 추가
+	public Lesson findLessonByIdWithLock(Long lessonId) {
+		return lessonRepository.findByIdWithLock(lessonId)
+			.orElseThrow(() -> new BusinessException(ErrorCode.LESSON_NOT_FOUND));
+	}
+
 	//레슨 신청 조회
 	public LessonApplication findApplicationById(Long applicationId) {
 		return lessonApplicationRepository.findById(applicationId)