[Fix] 상품 조회 시 N+1 쿼리 문제 해결 (#328)

* work

* work

* work

Author: yeeJin227

src/main/java/com/back/domain/product/product/repository/ProductCustomRepositoryImpl.java

@@ -80,24 +80,13 @@ public ProductListResponse findProducts(
             ));
         }
 
-        // QueryDSL로 DTO 매핑 + THUMBNAIL join
+        // QueryDSL로 엔티티 조회 + THUMBNAIL join
         var query = queryFactory
-                .select(Projections.constructor(
-                        ProductInfo.class, // dto 매핑
-                        p.productUuid, // 상품 uuid
-                        img.fileUrl, //썸네일 이미지 url
-                        p.brandName, // 브랜드명
-                        p.name, // 상품명
-                        p.price, // 가격
-                        p.discountRate,// 할인율
-                        p.price.subtract(p.price.multiply(p.discountRate).divide(100)), // 할인된 최종 가격
-                        Expressions.nullExpression(Double.class) // rating: 리뷰 연동 전이라서 일단 null로 함.
-                ))
+                .select(p)
                 .from(p)
-                .leftJoin(p.images, img) // left join
-                .on(img.fileType.eq(FileType.THUMBNAIL)) // type이 THUMBNAIL인 이미지만 JOIN
-                .where(builder) // 동적 조건 적용
-                .distinct(); // 중복 제거
+                .leftJoin(p.images, img).on(img.fileType.eq(FileType.THUMBNAIL))
+                .where(builder)
+                .distinct();
 
         // 정렬 처리
         if ("priceAsc".equals(sort)) query.orderBy(p.price.asc()); // 가격 낮은 순
@@ -107,12 +96,35 @@ public ProductListResponse findProducts(
         // 전체 건수 조회 (페이징용)
         long total = query.fetchCount();
 
-        // 페이징 적용
-        List<ProductInfo> products = query
-                .offset(pageable.getOffset()) // offset
-                .limit(pageable.getPageSize()) //limit
+        // 페이징 적용하여 엔티티 조회
+        List<com.back.domain.product.product.entity.Product> fetchedProducts = query
+                .offset(pageable.getOffset())
+                .limit(pageable.getPageSize())
                 .fetch();
 
+        // 엔티티를 DTO로 변환
+        List<ProductInfo> products = fetchedProducts.stream()
+                .map(product -> {
+                    String thumbnailUrl = product.getImages().stream()
+                            .filter(i -> i.getFileType() == FileType.THUMBNAIL)
+                            .findFirst()
+                            .map(com.back.domain.product.product.entity.ProductImage::getFileUrl)
+                            .orElse(null);
+
+                    return new ProductInfo(
+                            product.getProductUuid(),
+                            thumbnailUrl,
+                            product.getBrandName(),
+                            product.getName(),
+                            product.getPrice(),
+                            product.getDiscountRate(),
+                            product.getDiscountPrice(),
+                            product.getAverageRating()
+                    );
+                })
+                .toList();
+
+
         int totalPages = (int) Math.ceil((double) total / pageable.getPageSize());
 
         // 최종 DTO 반환

src/main/java/com/back/domain/product/product/repository/ProductRepository.java

@@ -35,43 +35,49 @@ public interface ProductRepository extends JpaRepository<Product, Long>, Product
     List<Product> findBySellingEndDateBefore(LocalDateTime dateTime);
 
     // 신상품 (최근 14일)
-    @Query("SELECT p FROM Product p " +
+    @Query("SELECT DISTINCT p FROM Product p " +
+            "LEFT JOIN FETCH p.images " +
             "WHERE p.createDate BETWEEN :fromDate AND :toDate " +
             "AND p.displayStatus = com.back.domain.product.product.entity.DisplayStatus.DISPLAYING " +
             "ORDER BY p.createDate DESC")
     List<Product> findRecentProducts(@Param("fromDate") LocalDateTime fromDate,
                                      @Param("toDate") LocalDateTime toDate);
 
     // 할인중 상품
-    @Query("SELECT p FROM Product p " +
+    @Query("SELECT DISTINCT p FROM Product p " +
+            "LEFT JOIN FETCH p.images " +
             "WHERE p.discountRate > 0 " +
             "AND p.displayStatus = com.back.domain.product.product.entity.DisplayStatus.DISPLAYING " +
             "ORDER BY p.discountRate DESC")
     List<Product> findOnSaleProducts();
 
     // 품절 임박 상품 (재고 5개 이하)
-    @Query("SELECT p FROM Product p " +
+    @Query("SELECT DISTINCT p FROM Product p " +
+            "LEFT JOIN FETCH p.images " +
             "WHERE p.stock <= 5 " +
             "AND p.displayStatus = com.back.domain.product.product.entity.DisplayStatus.DISPLAYING " +
             "ORDER BY p.stock ASC")
     List<Product> findLowStockProducts();
 
     // 재입고 상품
-    @Query("SELECT p FROM Product p " +
+    @Query("SELECT DISTINCT p FROM Product p " +
+            "LEFT JOIN FETCH p.images " +
             "WHERE p.isRestock = true " +
             "AND p.displayStatus = com.back.domain.product.product.entity.DisplayStatus.DISPLAYING " +
             "ORDER BY p.createDate DESC")
     List<Product> findRestockProducts();
 
     // 기획 상품
-    @Query("SELECT p FROM Product p " +
+    @Query("SELECT DISTINCT p FROM Product p " +
+            "LEFT JOIN FETCH p.images " +
             "WHERE p.isPlanned = true " +
             "AND p.displayStatus = com.back.domain.product.product.entity.DisplayStatus.DISPLAYING " +
             "ORDER BY p.createDate DESC")
     List<Product> findPlannedProducts();
 
     // 오픈 예정 상품
-    @Query("SELECT p FROM Product p " +
+    @Query("SELECT DISTINCT p FROM Product p " +
+            "LEFT JOIN FETCH p.images " +
             "WHERE p.sellingStartDate > :today " +
             "AND p.displayStatus = com.back.domain.product.product.entity.DisplayStatus.DISPLAYING " +
             "ORDER BY p.sellingStartDate ASC")

src/main/java/com/back/domain/product/product/service/ProductService.java

@@ -152,34 +152,39 @@ public List<ProductListResponse.ProductInfo> getAllNewProducts() {
     }
 
     /** 메인페이지 - 할인중 상품 */
+    @Transactional(readOnly = true)
     public List<ProductListResponse.ProductInfo> getOnSaleProducts() {
         List<Product> products = productRepository.findOnSaleProducts();
         if (products.isEmpty()) throw new ServiceException("404", "할인중인 상품이 존재하지 않습니다.");
         return products.stream().map(this::toProductInfo).toList();
     }
 
     /** 메인페이지 - 품절 임박 상품 */
+    @Transactional(readOnly = true)
     public List<ProductListResponse.ProductInfo> getLowStockProducts() {
         List<Product> products = productRepository.findLowStockProducts();
         if (products.isEmpty()) throw new ServiceException("404", "품절 임박 상품이 존재하지 않습니다.");
         return products.stream().map(this::toProductInfo).toList();
     }
 
     /** 메인페이지 - 재입고 상품 */
+    @Transactional(readOnly = true)
     public List<ProductListResponse.ProductInfo> getRestockProducts() {
         List<Product> products = productRepository.findRestockProducts();
         if (products.isEmpty()) throw new ServiceException("404", "재입고 상품이 존재하지 않습니다.");
         return products.stream().map(this::toProductInfo).toList();
     }
 
     /** 메인페이지 - 기획 상품 */
+    @Transactional(readOnly = true)
     public List<ProductListResponse.ProductInfo> getPlannedProducts() {
         List<Product> products = productRepository.findPlannedProducts();
         if (products.isEmpty()) throw new ServiceException("404", "기획 상품이 존재하지 않습니다.");
         return products.stream().map(this::toProductInfo).toList();
     }
 
     /** 메인페이지 - 오픈 예정 상품 */
+    @Transactional(readOnly = true)
     public List<ProductListResponse.ProductInfo> getUpcomingProducts() {
         LocalDateTime today = LocalDateTime.now();
         List<Product> products = productRepository.findUpcomingProducts(today);