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[Refactor] 질문 목록 조회 시 좋아요 여부 N+1 쿼리 개선 #162

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Merged
kkw610 merged 1 commit into from
Jun 2, 2026
Merged

[Refactor] 질문 목록 조회 시 좋아요 여부 N+1 쿼리 개선 #162

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11 changes: 11 additions & 0 deletions ...in/java/com/example/Piroin/project/domain/question/repository/QuestionLikeRepository.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,10 @@
import com.example.Piroin.project.domain.question.entity.QuestionLike;
import com.example.Piroin.project.domain.user.entity.User;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;

import java.util.List;
import java.util.Optional;

public interface QuestionLikeRepository extends JpaRepository<QuestionLike, Long> {
Expand All @@ -19,4 +22,12 @@ public interface QuestionLikeRepository extends JpaRepository<QuestionLike, Long
용도: 질문 상세 응답에 is_liked 필드 포함 시
*/
boolean existsByQuestionAndUser(Question question, User user);

// 특정 유저가 좋아요를 누른 질문 ID 목록을 한 번에 조회
// 용도: 질문 목록 조회 시 N+1 방지
@Query("SELECT ql.question.id FROM QuestionLike ql WHERE ql.question.id IN :questionIds AND ql.user = :user")
List<Long> findLikedQuestionIdsByQuestionIdsAndUser(
@Param("questionIds") List<Long> questionIds,
@Param("user") User user
);
}
42 changes: 29 additions & 13 deletions ...end/src/main/java/com/example/Piroin/project/domain/question/service/QuestionService.java
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Original file line number Diff line number Diff line change
Expand Up @@ -27,7 +27,9 @@
import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Set;
import java.util.Map;
import java.util.HashSet;
import java.util.stream.Collectors;

@Service
Expand Down Expand Up @@ -589,7 +591,7 @@ private QuestionResDTO.UnderstandingCheckResponse toUnderstandingCheckResponse(

private QuestionResDTO.QuestionGroupsResponse getQuestionGroups(StudySession session, User loginUser) {
List<Question> questions = questionRepository.findBySessionAndDeletedAtIsNull(session);
QuestionSummaryContext summaryContext = getQuestionSummaryContext(questions);
QuestionSummaryContext summaryContext = getQuestionSummaryContext(questions, loginUser);

List<QuestionResDTO.QuestionSummaryResponse> popularQuestions = questions.stream()
.filter(q -> !q.getIsResolved() && q.getLikeCount() >= POPULAR_LIKE_THRESHOLD)
Expand All @@ -616,7 +618,7 @@ private QuestionResDTO.QuestionSummaryResponse toQuestionSummaryResponse (
User loginUser
) {
Long questionId = question.getId();
boolean isLiked = questionLikeRepository.existsByQuestionAndUser(question, loginUser);
boolean isLiked = summaryContext.likedQuestionIds().contains(questionId);
boolean isMine = question.getUser().getId().equals(loginUser.getId());
return new QuestionResDTO.QuestionSummaryResponse(
questionId, question.getContent(), question.getImageUrl(),
Expand All @@ -632,9 +634,9 @@ private QuestionResDTO.QuestionSummaryResponse toQuestionSummaryResponse (
);
}

private QuestionSummaryContext getQuestionSummaryContext(List<Question> questions) {
private QuestionSummaryContext getQuestionSummaryContext(List<Question> questions, User loginUser) {
if (questions.isEmpty()) {
return new QuestionSummaryContext(Map.of(), Map.of());
return new QuestionSummaryContext(Map.of(), Map.of(), Set.of());
}

List<Long> questionIds = questions.stream()
Expand All @@ -651,14 +653,17 @@ private QuestionSummaryContext getQuestionSummaryContext(List<Question> question
questionCommentRepository.findPreviewCommentsByQuestionIds(questionIds)
.forEach(row -> {
Question question = questionsById.get(row.getQuestionId());
if (question == null) {
return;
}
if (question == null) return;
previewComments.computeIfAbsent(row.getQuestionId(), key -> new ArrayList<>())
.add(toPreviewCommentResponse(question, row));
});

return new QuestionSummaryContext(commentCounts, previewComments);
// 좋아요 여부를 질문마다 조회하는 대신 한 번에 배치 조회한다.
Set<Long> likedQuestionIds = new HashSet<>(
questionLikeRepository.findLikedQuestionIdsByQuestionIdsAndUser(questionIds, loginUser)
);

return new QuestionSummaryContext(commentCounts, previewComments, likedQuestionIds);
}

private QuestionResDTO.PreviewCommentResponse toPreviewCommentResponse(
Expand Down Expand Up @@ -692,16 +697,26 @@ private String getPreviewDisplayName(Question question, QuestionCommentRepositor
private void publishCommentCreatedEventAfterCommit(Question question) {
Long sessionId = question.getSession().getId();
Long questionId = question.getId();
QuestionSummaryContext summaryContext = getQuestionSummaryContext(List.of(question));

// 프론트가 전체 목록을 다시 조회하지 않고 해당 질문만 갱신할 수 있는 최소 데이터만 보낸다.
// 이벤트 발행용이라 좋아요 여부가 필요 없으므로 댓글 수/미리보기만 직접 조회
List<Long> questionIds = List.of(questionId);

Map<Long, Integer> commentCounts = new HashMap<>();
questionCommentRepository.countByQuestionIds(questionIds)
.forEach(row -> commentCounts.put(row.getQuestionId(), Math.toIntExact(row.getCommentCount())));

Map<Long, List<QuestionResDTO.PreviewCommentResponse>> previewComments = new HashMap<>();
questionCommentRepository.findPreviewCommentsByQuestionIds(questionIds)
.forEach(row -> previewComments.computeIfAbsent(row.getQuestionId(), key -> new ArrayList<>())
.add(toPreviewCommentResponse(question, row)));

QuestionResDTO.CommentCreatedEvent event = new QuestionResDTO.CommentCreatedEvent(
"COMMENT_CREATED",
sessionId,
questionId,
question.getIsResolved(),
summaryContext.commentCounts().getOrDefault(questionId, 0),
summaryContext.previewComments().getOrDefault(questionId, List.of())
commentCounts.getOrDefault(questionId, 0),
previewComments.getOrDefault(questionId, List.of())
);

publishAfterCommit(() -> questionEventService.publishCommentCreated(sessionId, event));
Expand Down Expand Up @@ -774,7 +789,8 @@ public void afterCommit() {

private record QuestionSummaryContext(
Map<Long, Integer> commentCounts,
Map<Long, List<QuestionResDTO.PreviewCommentResponse>> previewComments
Map<Long, List<QuestionResDTO.PreviewCommentResponse>> previewComments,
Set<Long> likedQuestionIds
) {
}
}
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