fix: 새 항목의 표시 순서를 개수가 아닌 마지막 순서 + 1로 정한다

src/main/java/com/bcsdlab/bcsdinternalapiv2/activity/service/AdminActivityCategoryService.java

@@ -39,7 +39,8 @@ public AdminActivityCategoryResponse createCategory(ActivityCategoryCreateReques
             throw new ActivityException(ActivityExceptionType.CATEGORY_SLUG_DUPLICATED);
         }
 
-        int displayOrder = activityCategoryRepository.findAllByOrderByDisplayOrderAsc().size();
+        int displayOrder = DisplayOrders.next(activityCategoryRepository.findAllByOrderByDisplayOrderAsc(),
+                ActivityCategory::getDisplayOrder);
         ActivityCategory category = activityCategoryRepository.save(ActivityCategory.builder()
                 .slug(request.slug())
                 .name(request.name())

src/main/java/com/bcsdlab/bcsdinternalapiv2/curriculum/service/AdminCurriculumService.java

@@ -8,6 +8,7 @@
 import com.bcsdlab.bcsdinternalapiv2.curriculum.model.Curriculum;
 import com.bcsdlab.bcsdinternalapiv2.curriculum.repository.CurriculumRepository;
 import com.bcsdlab.bcsdinternalapiv2.global.controller.dto.request.PublishRequest;
+import com.bcsdlab.bcsdinternalapiv2.global.util.DisplayOrders;
 import com.bcsdlab.bcsdinternalapiv2.track.exception.TrackException;
 import com.bcsdlab.bcsdinternalapiv2.track.exception.TrackExceptionType;
 import com.bcsdlab.bcsdinternalapiv2.track.model.TrackPage;
@@ -59,7 +60,9 @@ public AdminCurriculumSummaryResponse createCurriculum(Long trackPageId, Curricu
             throw new CurriculumException(CurriculumExceptionType.NAME_REQUIRED);
         }
 
-        int displayOrder = curriculumRepository.findAllByTrackPage_IdOrderByDisplayOrderAsc(trackPageId).size();
+        int displayOrder = DisplayOrders.next(
+                curriculumRepository.findAllByTrackPage_IdOrderByDisplayOrderAsc(trackPageId),
+                Curriculum::getDisplayOrder);
         Curriculum curriculum = curriculumRepository.save(Curriculum.builder()
                 .trackPage(trackPage)
                 .name(name)

src/main/java/com/bcsdlab/bcsdinternalapiv2/curriculum/service/AdminCurriculumTreeService.java

@@ -80,7 +80,9 @@ public CurriculumWeekResponse createWeek(Long curriculumId, WeekRequest request,
                 .orElseThrow(() -> new CurriculumException(CurriculumExceptionType.CURRICULUM_NOT_FOUND));
         requireCurriculumAccess(memberId, curriculum.getTrackPage());
 
-        int displayOrder = curriculumWeekRepository.findAllByCurriculum_IdOrderByDisplayOrderAsc(curriculumId).size();
+        int displayOrder = DisplayOrders.next(
+                curriculumWeekRepository.findAllByCurriculum_IdOrderByDisplayOrderAsc(curriculumId),
+                CurriculumWeek::getDisplayOrder);
         CurriculumWeek week = curriculumWeekRepository.save(CurriculumWeek.builder()
                 .curriculum(curriculum)
                 .weekFrom(request.weekFrom())
@@ -124,7 +126,8 @@ public void reorderWeeks(Long curriculumId, OrderRequest request, Long memberId)
     public CurriculumTopicResponse createTopic(Long weekId, TopicRequest request, Long memberId) {
         CurriculumWeek week = findWeekOrThrow(weekId);
         requireCurriculumAccess(memberId, week.getCurriculum().getTrackPage());
-        int displayOrder = curriculumTopicRepository.findAllByWeek_IdOrderByDisplayOrderAsc(weekId).size();
+        int displayOrder = DisplayOrders.next(curriculumTopicRepository.findAllByWeek_IdOrderByDisplayOrderAsc(weekId),
+                CurriculumTopic::getDisplayOrder);
         CurriculumTopic topic = curriculumTopicRepository.save(CurriculumTopic.builder()
                 .week(week)
                 .title(request.title())

src/main/java/com/bcsdlab/bcsdinternalapiv2/game/service/AdminGameMemberService.java

@@ -69,7 +69,8 @@ public List<AdminGameMemberResponse> attachMembers(Long gameId, GameMembersAttac
             }
         }
 
-        int nextOrder = gameMemberRepository.findAllByGame_IdOrderByDisplayOrderAsc(gameId).size();
+        int nextOrder = DisplayOrders.next(gameMemberRepository.findAllByGame_IdOrderByDisplayOrderAsc(gameId),
+                GameMember::getDisplayOrder);
         for (Long memberId : memberIds) {
             gameMemberRepository.save(GameMember.builder()
                     .game(game)

src/main/java/com/bcsdlab/bcsdinternalapiv2/game/service/AdminGameService.java

@@ -102,7 +102,8 @@ public AdminGameDetailResponse createGame(GameCreateRequest request, Long member
                 .oneLiner(request.oneLiner())
                 .track(track)
                 .teamLabel(request.teamLabel())
-                .displayOrder((int) gameRepository.count())
+                .displayOrder(DisplayOrders.next(gameRepository.findAllByOrderByDisplayOrderAsc(),
+                        Game::getDisplayOrder))
                 .published(false)
                 .build();
 

src/main/java/com/bcsdlab/bcsdinternalapiv2/global/util/DisplayOrders.java

@@ -8,6 +8,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.ToIntFunction;
 
 /**
  * {@code display_order} 재부여 순수 함수. 특정 엔티티 타입에 의존하지 않는다 —
@@ -22,6 +23,19 @@ public final class DisplayOrders {
     private DisplayOrders() {
     }
 
+    /**
+     * 새 항목의 display_order. 삭제가 순서를 다시 매기지 않아 번호에 빈칸이 생기므로, 개수가 아니라
+     * 마지막 순서 + 1이다(개수를 쓰면 기존 항목과 순서가 겹친다).
+     *
+     * @param siblingsInOrder 같은 부모 아래 형제 항목, display_order 오름차순
+     */
+    public static <T> int next(List<T> siblingsInOrder, ToIntFunction<T> displayOrder) {
+        if (siblingsInOrder.isEmpty()) {
+            return 0;
+        }
+        return displayOrder.applyAsInt(siblingsInOrder.getLast()) + 1;
+    }
+
     /**
      * @param requestedIds 새 순서대로 나열된 id 목록 (배열 인덱스가 곧 새 display_order)
      * @param existingIds  현재 그 부모 아래 존재하는 전체 id 집합

src/main/java/com/bcsdlab/bcsdinternalapiv2/home/service/AdminMentorSlotService.java

@@ -44,7 +44,8 @@ public List<AdminMentorSlotResponse> addSlot(MentorSlotCreateRequest request) {
             throw new HomeException(HomeExceptionType.MENTOR_ALREADY_ASSIGNED);
         }
 
-        int nextOrder = (int) mentorSlotRepository.count();
+        int nextOrder = DisplayOrders.next(mentorSlotRepository.findAllByOrderByDisplayOrderAsc(),
+                MentorSlot::getDisplayOrder);
         mentorSlotRepository.save(MentorSlot.builder().member(member).displayOrder(nextOrder).build());
         return getSlots();
     }

src/main/java/com/bcsdlab/bcsdinternalapiv2/home/service/AdminQnaService.java

@@ -35,7 +35,8 @@ public AdminQnaResponse createQnaItem(QnaCreateRequest request) {
         QnaItem saved = qnaItemRepository.save(QnaItem.builder()
                 .question(request.question())
                 .answer(request.answer())
-                .displayOrder((int) qnaItemRepository.count())
+                .displayOrder(DisplayOrders.next(qnaItemRepository.findAllByOrderByDisplayOrderAsc(),
+                        QnaItem::getDisplayOrder))
                 .published(true)
                 .build());
         return AdminQnaResponse.from(saved);

src/main/java/com/bcsdlab/bcsdinternalapiv2/track/service/AdminTrackPageMemberService.java

@@ -68,7 +68,9 @@ public List<AdminTrackPageMemberResponse> attachMembers(Long trackPageId, TrackP
             }
         }
 
-        int nextOrder = trackPageMemberRepository.findAllByTrackPage_IdOrderByDisplayOrderAsc(trackPageId).size();
+        int nextOrder = DisplayOrders.next(
+                trackPageMemberRepository.findAllByTrackPage_IdOrderByDisplayOrderAsc(trackPageId),
+                TrackPageMember::getDisplayOrder);
         for (Long memberId : memberIds) {
             trackPageMemberRepository.save(TrackPageMember.builder()
                     .trackPage(trackPage)

src/main/java/com/bcsdlab/bcsdinternalapiv2/track/service/AdminTrackPageService.java

@@ -108,7 +108,8 @@ public AdminTrackPageDetailResponse createTrackPage(TrackPageCreateRequest reque
                 .slug(slug)
                 .displayName(request.displayName())
                 .tagline(request.tagline())
-                .displayOrder((int) trackPageRepository.count())
+                .displayOrder(DisplayOrders.next(trackPageRepository.findAllByOrderByDisplayOrderAsc(),
+                        TrackPage::getDisplayOrder))
                 .published(true)
                 .build();
 

src/test/java/com/bcsdlab/bcsdinternalapiv2/global/DisplayOrdersTest.java

@@ -0,0 +1,23 @@
+package com.bcsdlab.bcsdinternalapiv2.global;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.bcsdlab.bcsdinternalapiv2.global.util.DisplayOrders;
+import java.util.List;
+import java.util.function.ToIntFunction;
+import org.junit.jupiter.api.Test;
+
+class DisplayOrdersTest {
+
+    private static final ToIntFunction<Integer> SELF = Integer::intValue;
+
+    @Test
+    void 형제가_없으면_0이다() {
+        assertThat(DisplayOrders.next(List.of(), SELF)).isZero();
+    }
+
+    @Test
+    void 삭제로_빈_번호가_있어도_마지막_순서_다음이다() {
+        assertThat(DisplayOrders.next(List.of(0, 2), SELF)).isEqualTo(3);
+    }
+}

src/test/java/com/bcsdlab/bcsdinternalapiv2/home/AdminQnaAndRecruitLinkIntegrationTest.java

@@ -1,5 +1,7 @@
 package com.bcsdlab.bcsdinternalapiv2.home;
 
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.delete;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.patch;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
@@ -21,6 +23,8 @@
 import com.bcsdlab.bcsdinternalapiv2.track.model.TrackMaster;
 import com.bcsdlab.bcsdinternalapiv2.track.repository.TrackMasterRepository;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import java.util.ArrayList;
+import java.util.List;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
@@ -186,4 +190,35 @@ private String login(String studentNumber) throws Exception {
                 .andReturn().getResponse().getContentAsString();
         return objectMapper.readTree(body).get("accessToken").asText();
     }
+
+    @Test
+    @DisplayName("Q&A를 지운 뒤 새로 만들면 남은 항목과 순서가 겹치지 않고 맨 뒤에 붙는다")
+    void 삭제_후_생성한_Q_A는_맨_뒤에_붙는다() throws Exception {
+        long first = createQna("첫 질문");
+        long second = createQna("둘째 질문");
+        createQna("셋째 질문");
+
+        mockMvc.perform(delete("/v1/admin/qna/" + second).header("Authorization", "Bearer " + adminToken))
+                .andExpect(status().isNoContent());
+        long fourth = createQna("넷째 질문");
+
+        String list = mockMvc.perform(get("/v1/admin/qna").header("Authorization", "Bearer " + adminToken))
+                .andExpect(status().isOk())
+                .andReturn().getResponse().getContentAsString();
+        List<Integer> orders = new ArrayList<>();
+        objectMapper.readTree(list).forEach(item -> orders.add(item.get("displayOrder").asInt()));
+        assertThat(orders).doesNotHaveDuplicates();
+        assertThat(objectMapper.readTree(list).get(0).get("id").asLong()).isEqualTo(first);
+        assertThat(objectMapper.readTree(list).get(2).get("id").asLong()).isEqualTo(fourth);
+    }
+
+    private long createQna(String question) throws Exception {
+        String body = mockMvc.perform(post("/v1/admin/qna")
+                        .header("Authorization", "Bearer " + adminToken)
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"question\":\"%s\",\"answer\":\"답변\"}".formatted(question)))
+                .andExpect(status().isCreated())
+                .andReturn().getResponse().getContentAsString();
+        return objectMapper.readTree(body).get("id").asLong();
+    }
 }