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refactor: 채팅방 관련 n + 1 문제 개선 #477

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Merged
Gyuhyeok99 merged 2 commits into from
Aug 28, 2025
Merged

refactor: 채팅방 관련 n + 1 문제 개선 #477

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2ae9c62
refactor: n + 1 문제 개선
Gyuhyeok99 Aug 24, 2025
62abb86
refactor: 함수 가독성 개선
Gyuhyeok99 Aug 24, 2025
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24 changes: 24 additions & 0 deletions src/main/java/com/example/solidconnection/chat/dto/ChatRoomData.java
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@@ -0,0 +1,24 @@
package com.example.solidconnection.chat.dto;

import com.example.solidconnection.chat.domain.ChatMessage;
import com.example.solidconnection.siteuser.domain.SiteUser;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public record ChatRoomData(
Map<Long, ChatMessage> latestMessages,
Map<Long, Long> unreadCounts,
Map<Long, SiteUser> partnerUsers
) {

public static ChatRoomData from(List<ChatMessage> latestMessages,
List<UnreadCountDto> unreadCounts,
List<SiteUser> partnerUsers) {
return new ChatRoomData(
latestMessages.stream().collect(Collectors.toMap(msg -> msg.getChatRoom().getId(), msg -> msg)),
unreadCounts.stream().collect(Collectors.toMap(UnreadCountDto::chatRoomId, UnreadCountDto::count)),
partnerUsers.stream().collect(Collectors.toMap(SiteUser::getId, user -> user))
);
}
}
8 changes: 8 additions & 0 deletions src/main/java/com/example/solidconnection/chat/dto/UnreadCountDto.java
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@@ -0,0 +1,8 @@
package com.example.solidconnection.chat.dto;

public record UnreadCountDto(
long chatRoomId,
long count
) {

}
33 changes: 31 additions & 2 deletions src/main/java/com/example/solidconnection/chat/repository/ChatMessageRepository.java
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@@ -1,7 +1,8 @@
package com.example.solidconnection.chat.repository;

import com.example.solidconnection.chat.domain.ChatMessage;
import java.util.Optional;
import com.example.solidconnection.chat.dto.UnreadCountDto;
import java.util.List;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Slice;
import org.springframework.data.jpa.repository.JpaRepository;
Expand All @@ -18,5 +19,33 @@ public interface ChatMessageRepository extends JpaRepository<ChatMessage, Long>
""")
Slice<ChatMessage> findByRoomIdWithPaging(@Param("roomId") long roomId, Pageable pageable);

Optional<ChatMessage> findFirstByChatRoomIdOrderByCreatedAtDesc(long chatRoomId);
@Query("""
SELECT cm FROM ChatMessage cm
WHERE cm.id IN (
SELECT MAX(cm2.id)
FROM ChatMessage cm2
WHERE cm2.chatRoom.id IN :chatRoomIds
GROUP BY cm2.chatRoom.id
)
""")
List<ChatMessage> findLatestMessagesByChatRoomIds(@Param("chatRoomIds") List<Long> chatRoomIds);
Comment on lines +22 to +31
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💡 Verification agent

🧩 Analysis chain

최신 메시지 선정 기준을 id → createdAt로 통일해 의미적 정합성 보장.

    1. 의미 불일치. 현재 쿼리는 MAX(id)로 "최신"을 결정하지만, ChatRoomRepository는 createdAt 기준으로 정렬합니다. 두 기준이 불일치하면 복원력 없는 결과가 됩니다(시퀀스 점프·데이터 마이그레이션·수동 삽입 시).
    1. 정확성. "최신"의 정의가 도메인적으로 생성시각(createdAt)이라면 쿼리도 동일 기준을 써야 합니다.
    1. 동률 처리. 동일 createdAt이 드물지만 가능하므로, 동률 시 더 큰 id를 고르는 보조 기준을 서비스/조합 단계에서 처리하는 것이 안전합니다(아래 ChatRoomData 개선안에 병행 제안).
    1. 빈 목록. IN (:chatRoomIds)로 빈 리스트가 들어오면 프로바이더에 따라 예외가 날 수 있어 호출부에서 빈 리스트 가드가 필요합니다.

ChatMessage의 @GeneratedValue 전략과 createdAt 세터·감사 필드 전략을 확인해 일관된 시간 정렬이 가능한지 점검해 주세요.

아래와 같이 쿼리를 createdAt 기준으로 바꾸는 것을 권장합니다.

-    @Query("""
-           SELECT cm FROM ChatMessage cm
-           WHERE cm.id IN (
-               SELECT MAX(cm2.id)
-               FROM ChatMessage cm2
-               WHERE cm2.chatRoom.id IN :chatRoomIds
-               GROUP BY cm2.chatRoom.id
-           )
-           """)
+    @Query("""
+           SELECT cm FROM ChatMessage cm
+           WHERE cm.chatRoom.id IN :chatRoomIds
+           AND cm.createdAt = (
+               SELECT MAX(cm2.createdAt)
+               FROM ChatMessage cm2
+               WHERE cm2.chatRoom = cm.chatRoom
+           )
+           """)
     List<ChatMessage> findLatestMessagesByChatRoomIds(@Param("chatRoomIds") List<Long> chatRoomIds);

🏁 Script executed:

#!/bin/bash
# ChatMessage ID/시간 필드 정의 확인
rg -n -C3 'class\s+ChatMessage\b'
rg -n -C2 '@GeneratedValue|createdAt' --type=java

Length of output: 37996

ChatMessageRepository의 최신 메시지 선별 기준을 createdAt으로 통일하기

  1. 쿼리 기준 통일

    • ChatRoomRepository는 메시지 최신 순 선별에 createdAt을 사용합니다.
    • 반면 ChatMessageRepository는 MAX(id)로 최신 메시지를 선택하고 있어 두 결과가 불일치할 수 있습니다.
    • 아래 코드처럼 쿼리를 createdAt 기준으로 수정해주세요.
    -@Query("""
-       SELECT cm FROM ChatMessage cm
-       WHERE cm.id IN (
-           SELECT MAX(cm2.id)
-           FROM ChatMessage cm2
-           WHERE cm2.chatRoom.id IN :chatRoomIds
-           GROUP BY cm2.chatRoom.id
-       )
-       """)
+@Query("""
+       SELECT cm FROM ChatMessage cm
+       WHERE cm.chatRoom.id IN :chatRoomIds
+       AND cm.createdAt = (
+           SELECT MAX(cm2.createdAt)
+           FROM ChatMessage cm2
+           WHERE cm2.chatRoom = cm.chatRoom
+       )
+       """)
List<ChatMessage> findLatestMessagesByChatRoomIds(@Param("chatRoomIds") List<Long> chatRoomIds);

  2. createdAt 필드 설정 확인

    • ChatMessage는 BaseEntity를 상속받아 @PrePersist에서 createdAt이 ZonedDateTime.now(UTC).truncatedTo(MICROS)로 자동 설정됩니다.
    • 따라서 createdAt을 비교 기준으로 사용하는 것이 도메인적으로도 일관되고 안전합니다.

  3. 빈 리스트 처리

    • IN절에 빈 컬렉션(chatRoomIds)이 들어갈 경우 일부 JPA 구현체에서 예외가 발생할 수 있습니다.
    • 호출부에서 빈 리스트인 경우 바로 빈 결과를 반환하거나, 레포지토리 호출 전 guard 로직을 추가해주세요.

  4. 동률 처리

    • 동일한 createdAt을 가지는 메시지가 극히 드물지만 가능하므로, 동률 시 더 큰 id를 선택하는 보조 로직을 서비스 레이어에서 추가 적용을 권장합니다.
  • 대상 파일: src/main/java/com/example/solidconnection/chat/repository/ChatMessageRepository.java (22–31번 라인)
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
@Query("""
SELECT cm FROM ChatMessage cm
WHERE cm.id IN (
SELECT MAX(cm2.id)
FROM ChatMessage cm2
WHERE cm2.chatRoom.id IN :chatRoomIds
GROUP BY cm2.chatRoom.id
)
""")
List<ChatMessage> findLatestMessagesByChatRoomIds(@Param("chatRoomIds") List<Long> chatRoomIds);
@Query("""
SELECT cm FROM ChatMessage cm
WHERE cm.chatRoom.id IN :chatRoomIds
AND cm.createdAt = (
SELECT MAX(cm2.createdAt)
FROM ChatMessage cm2
WHERE cm2.chatRoom = cm.chatRoom
)
""")
List<ChatMessage> findLatestMessagesByChatRoomIds(@Param("chatRoomIds") List<Long> chatRoomIds);
🤖 Prompt for AI Agents 
In
src/main/java/com/example/solidconnection/chat/repository/ChatMessageRepository.java
around lines 22-31, the repository currently selects latest messages by MAX(id)
which conflicts with ChatRoomRepository that uses createdAt; change the JPQL to
select messages whose createdAt equals the MAX(cm2.createdAt) grouped by
cm2.chatRoom.id (i.e. use MAX(cm2.createdAt) in the subquery and compare
cm.createdAt), keep the method signature and @Param unchanged, and ensure
callers guard against an empty chatRoomIds (return empty list before calling
repository) to avoid IN () issues; optionally handle tie-breakers (same
createdAt) in the service layer by selecting the message with the larger id when
createdAt values are equal.


@Query("""
SELECT new com.example.solidconnection.chat.dto.UnreadCountDto(
cm.chatRoom.id,
COUNT(cm)
)
FROM ChatMessage cm
LEFT JOIN ChatReadStatus crs ON crs.chatRoomId = cm.chatRoom.id
AND crs.chatParticipantId = (
SELECT cp.id FROM ChatParticipant cp
WHERE cp.chatRoom.id = cm.chatRoom.id
AND cp.siteUserId = :userId
)
WHERE cm.chatRoom.id IN :chatRoomIds
AND cm.senderId != :userId
AND (crs.updatedAt IS NULL OR cm.createdAt > crs.updatedAt)
GROUP BY cm.chatRoom.id
""")
List<UnreadCountDto> countUnreadMessagesBatch(@Param("chatRoomIds") List<Long> chatRoomIds, @Param("userId") long userId);
}
27 changes: 9 additions & 18 deletions src/main/java/com/example/solidconnection/chat/repository/ChatRoomRepository.java
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Expand Up @@ -9,30 +9,21 @@
public interface ChatRoomRepository extends JpaRepository<ChatRoom, Long> {

@Query("""
SELECT cr FROM ChatRoom cr
JOIN cr.chatParticipants cp
WHERE cp.siteUserId = :userId AND cr.isGroup = false
SELECT DISTINCT cr FROM ChatRoom cr
JOIN FETCH cr.chatParticipants
WHERE cr.id IN (
SELECT DISTINCT cp2.chatRoom.id
FROM ChatParticipant cp2
WHERE cp2.siteUserId = :userId
)
AND cr.isGroup = false
ORDER BY (
SELECT MAX(cm.createdAt)
FROM ChatMessage cm
WHERE cm.chatRoom = cr
) DESC NULLS LAST
""")
List<ChatRoom> findOneOnOneChatRoomsByUserId(@Param("userId") long userId);

@Query("""
SELECT COUNT(cm) FROM ChatMessage cm
LEFT JOIN ChatReadStatus crs ON crs.chatRoomId = cm.chatRoom.id
AND crs.chatParticipantId = (
SELECT cp.id FROM ChatParticipant cp
WHERE cp.chatRoom.id = :chatRoomId
AND cp.siteUserId = :userId
)
WHERE cm.chatRoom.id = :chatRoomId
AND cm.senderId != :userId
AND (crs.updatedAt IS NULL OR cm.createdAt > crs.updatedAt)
""")
long countUnreadMessages(@Param("chatRoomId") long chatRoomId, @Param("userId") long userId);
List<ChatRoom> findOneOnOneChatRoomsByUserIdWithParticipants(@Param("userId") long userId);

boolean existsByMentoringId(long mentoringId);
}
56 changes: 39 additions & 17 deletions src/main/java/com/example/solidconnection/chat/service/ChatService.java
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Expand Up @@ -21,11 +21,11 @@
import com.example.solidconnection.chat.repository.ChatRoomRepository;
import com.example.solidconnection.common.dto.SliceResponse;
import com.example.solidconnection.common.exception.CustomException;
import com.example.solidconnection.chat.dto.ChatRoomData;
import com.example.solidconnection.siteuser.domain.SiteUser;
import com.example.solidconnection.siteuser.repository.SiteUserRepository;
import java.time.ZonedDateTime;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import org.springframework.context.annotation.Lazy;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Slice;
Expand Down Expand Up @@ -60,28 +60,50 @@ public ChatService(ChatRoomRepository chatRoomRepository,

@Transactional(readOnly = true)
public ChatRoomListResponse getChatRooms(long siteUserId) {
// todo : n + 1 문제 해결 필요!
List<ChatRoom> chatRooms = chatRoomRepository.findOneOnOneChatRoomsByUserId(siteUserId);
List<ChatRoomResponse> chatRoomInfos = chatRooms.stream()
.map(chatRoom -> toChatRoomResponse(chatRoom, siteUserId))
List<ChatRoom> chatRooms = chatRoomRepository.findOneOnOneChatRoomsByUserIdWithParticipants(siteUserId);

if (chatRooms.isEmpty()) {
return ChatRoomListResponse.of(Collections.emptyList());
}

ChatRoomData chatRoomData = getChatRoomData(chatRooms, siteUserId);

List<ChatRoomResponse> responses = chatRooms.stream()
.map(chatRoom -> createChatRoomResponse(chatRoom, siteUserId, chatRoomData))
.toList();
return ChatRoomListResponse.of(chatRoomInfos);

return ChatRoomListResponse.of(responses);
}

private ChatRoomResponse toChatRoomResponse(ChatRoom chatRoom, long siteUserId) {
Optional<ChatMessage> latestMessage = chatMessageRepository.findFirstByChatRoomIdOrderByCreatedAtDesc(chatRoom.getId());
String lastChatMessage = latestMessage.map(ChatMessage::getContent).orElse("");
ZonedDateTime lastReceivedTime = latestMessage.map(ChatMessage::getCreatedAt).orElse(null);
private ChatRoomData getChatRoomData(List<ChatRoom> chatRooms, long siteUserId) {
List<Long> chatRoomIds = chatRooms.stream().map(ChatRoom::getId).toList();
List<Long> partnerUserIds = chatRooms.stream()
.map(chatRoom -> findPartner(chatRoom, siteUserId).getSiteUserId())
.toList();

ChatParticipant partnerParticipant = findPartner(chatRoom, siteUserId);
return ChatRoomData.from(
chatMessageRepository.findLatestMessagesByChatRoomIds(chatRoomIds),
chatMessageRepository.countUnreadMessagesBatch(chatRoomIds, siteUserId),
siteUserRepository.findAllByIdIn(partnerUserIds)
);
}

SiteUser siteUser = siteUserRepository.findById(partnerParticipant.getSiteUserId())
.orElseThrow(() -> new CustomException(USER_NOT_FOUND));
ChatParticipantResponse partner = ChatParticipantResponse.of(siteUser.getId(), siteUser.getNickname(), siteUser.getProfileImageUrl());
private ChatRoomResponse createChatRoomResponse(ChatRoom chatRoom, long siteUserId, ChatRoomData chatRoomData) {
ChatMessage latestMessage = chatRoomData.latestMessages().get(chatRoom.getId());
ChatParticipant partner = findPartner(chatRoom, siteUserId);
SiteUser partnerUser = chatRoomData.partnerUsers().get(partner.getSiteUserId());

long unReadCount = chatRoomRepository.countUnreadMessages(chatRoom.getId(), siteUserId);
if (partnerUser == null) {
throw new CustomException(USER_NOT_FOUND);
}

return ChatRoomResponse.of(chatRoom.getId(), lastChatMessage, lastReceivedTime, partner, unReadCount);
return ChatRoomResponse.of(
chatRoom.getId(),
latestMessage != null ? latestMessage.getContent() : "",
latestMessage != null ? latestMessage.getCreatedAt() : null,
ChatParticipantResponse.of(partnerUser.getId(), partnerUser.getNickname(), partnerUser.getProfileImageUrl()),
chatRoomData.unreadCounts().getOrDefault(chatRoom.getId(), 0L)
);
}

private ChatParticipant findPartner(ChatRoom chatRoom, long siteUserId) {
Expand Down
2 changes: 2 additions & 0 deletions src/main/java/com/example/solidconnection/siteuser/repository/SiteUserRepository.java
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Expand Up @@ -19,4 +19,6 @@ public interface SiteUserRepository extends JpaRepository<SiteUser, Long> {

@Query("SELECT u FROM SiteUser u WHERE u.quitedAt <= :cutoffDate")
List<SiteUser> findUsersToBeRemoved(@Param("cutoffDate") LocalDate cutoffDate);

List<SiteUser> findAllByIdIn(List<Long> ids);
}
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