Querydsl projections 사용시 트러블 슈팅

Querydsl Projections 사용시 발생한 문제 해결 과정

프로젝트 진행 중 발생한 오류에 관해 기록했습니다.

QueryDsl에서 Projections.bean() 사용 시 발생하는 ExpressionException 일으킨 기존 코드

package com.WalkiePaw.domain.chatroom.repository;

import com.WalkiePaw.presentation.domain.chatroom.dto.ChatroomListResponse;
import com.querydsl.core.types.Projections;
import com.querydsl.jpa.impl.JPAQueryFactory;
import lombok.RequiredArgsConstructor;
import org.springframework.stereotype.Repository;

import java.util.List;

import static com.WalkiePaw.domain.chatroom.entity.QChatroom.*;

@Repository
@RequiredArgsConstructor
public class ChatroomRepositoryOverrideImpl implements ChatroomRepositoryOverride {

    private final JPAQueryFactory jpaQueryFactory;

    @Override
    public List<ChatroomListResponse> findByMemberId(final Integer memberId) {
        return jpaQueryFactory
                .select(Projections.fields(ChatroomListResponse.class,
                        chatroom.id, chatroom.board.location, chatroom.member.nickname
                        , chatroom.latestMessage, chatroom.unreadCount
                ))
                .from(chatroom)
                .where(chatroom.board.id.eq(memberId).or(chatroom.member.id.eq(memberId)))
                .fetch();
    }
}

---

에러 발생

Projections.bean()은 기본 생성자와 setter를 기반으로 동작한다, 그래서 해당 DTO에 기본생성자가 없으면면 에러가 발생!!!

또한 setter가 없다면 DTO의 필드에 값이 할당되지 못해서 모든 필드가 null이 되므로 주의해야한다.

오류 해결 전 ChatroomListResponse 코드

package com.WalkiePaw.presentation.domain.chatroom.dto;

import com.WalkiePaw.domain.chatroom.entity.Chatroom;
import lombok.AllArgsConstructor;
import lombok.Data;


@Data
@AllArgsConstructor
public class ChatroomListResponse {
    private final Integer id;
    private final String location;
    private final String nickname;
    private final String latestMessage;
    private final int unreadCount;
    
    

    public static ChatroomListResponse from(final Chatroom chatroom) {
        return new ChatroomListResponse(chatroom.getId(), chatroom.getBoard().getLocation(),
                 chatroom.getMember().getNickname(), chatroom.getLatestMessage(), chatroom.getUnreadCount());
    }
}

오류 해결 후 ChatroomListResponse 코드 🧏🏻‍♀️

package com.WalkiePaw.presentation.domain.chatroom.dto;

import com.WalkiePaw.domain.chatroom.entity.Chatroom;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;


@Data
@AllArgsConstructor
@NoArgsConstructor
public class ChatroomListResponse {
    private Integer id;
    private String location;
    private String nickname;
    private String latestMessage;
    private int unreadCount;

    public static ChatroomListResponse from(final Chatroom chatroom) {
        return new ChatroomListResponse(chatroom.getId(), chatroom.getBoard().getLocation(),
                 chatroom.getMember().getNickname(), chatroom.getLatestMessage(), chatroom.getUnreadCount());
    }
}

🧠 결론 : Projection에서 사용할 DTO에는 @NoArgsConstructor와 @Setter를 꼭 붙이자