feat: 나의 수강중인 스터디 조회 API 추가

src/main/java/com/gdschongik/gdsc/domain/study/api/StudentStudyController.java

@@ -2,6 +2,7 @@
 
 import com.gdschongik.gdsc.domain.study.application.StudentStudyService;
 import com.gdschongik.gdsc.domain.study.dto.request.StudyAttendCreateRequest;
+import com.gdschongik.gdsc.domain.study.dto.response.StudentMyCurrentStudyResponse;
 import com.gdschongik.gdsc.domain.study.dto.response.StudyApplicableResponse;
 import io.swagger.v3.oas.annotations.Operation;
 import io.swagger.v3.oas.annotations.tags.Tag;
@@ -52,4 +53,11 @@ public ResponseEntity<Void> attend(
         studentStudyService.attend(studyDetailId, request);
         return ResponseEntity.ok().build();
     }
+
+    @Operation(summary = "내 수강중인 스터디 조회", description = "나의 수강 중인 스터디를 조회합니다.")
+    @GetMapping("/me/ongoing")
+    public ResponseEntity<StudentMyCurrentStudyResponse> getMyCurrentStudy() {
+        StudentMyCurrentStudyResponse response = studentStudyService.getMyCurrentStudy();
+        return ResponseEntity.ok(response);
+    }
 }

src/main/java/com/gdschongik/gdsc/domain/study/application/StudentStudyService.java

@@ -11,6 +11,7 @@
 import com.gdschongik.gdsc.domain.study.domain.Attendance;
 import com.gdschongik.gdsc.domain.study.domain.AttendanceValidator;
 import com.gdschongik.gdsc.domain.study.dto.request.StudyAttendCreateRequest;
+import com.gdschongik.gdsc.domain.study.dto.response.StudentMyCurrentStudyResponse;
 import com.gdschongik.gdsc.domain.study.dto.response.StudyApplicableResponse;
 import com.gdschongik.gdsc.domain.study.dto.response.StudyResponse;
 import com.gdschongik.gdsc.global.exception.CustomException;
@@ -100,4 +101,14 @@ public void attend(Long studyDetailId, StudyAttendCreateRequest request) {
 
         log.info("[StudyService] 스터디 출석: attendanceId={}", attendance.getId());
     }
+
+    @Transactional(readOnly = true)
+    public StudentMyCurrentStudyResponse getMyCurrentStudy() {
+        Member currentMember = memberUtil.getCurrentMember();
+        StudyHistory studyHistory = studyHistoryRepository.findAllByMentee(currentMember).stream()
+                .filter(s -> s.getStudy().isStudyOngoing())
+                .findFirst()
+                .orElse(null);
+        return StudentMyCurrentStudyResponse.from(studyHistory);
+    }
 }

src/main/java/com/gdschongik/gdsc/domain/study/dto/response/StudentMyCurrentStudyResponse.java

@@ -0,0 +1,12 @@
+package com.gdschongik.gdsc.domain.study.dto.response;
+
+import com.gdschongik.gdsc.domain.study.domain.StudyHistory;
+
+public record StudentMyCurrentStudyResponse(Long studyId) {
+    public static StudentMyCurrentStudyResponse from(StudyHistory studyHistory) {
+        if (studyHistory == null) {
+            return new StudentMyCurrentStudyResponse(null);
+        }
+        return new StudentMyCurrentStudyResponse(studyHistory.getStudy().getId());
+    }
+}