JPA 조인

패치조인

// 컨트롤러
    @GetMapping("/api/v3/simple-orders")
    public List<SimpleOrderDto> ordersV3(){
        List<Order> orders = orderRepository.findAllWithMemberDelivery();
        List<SimpleOrderDto> result = orders.stream()
                .map(o -> new SimpleOrderDto(o))
                .collect(Collectors.toList());
        return result;
    }
	
    // DB 패치조인 조회
	public List<Order> findAllWithMemberDelivery() {
        return em.createQuery(
                "select o from Order o" +
                        " join fetch o.member m" +
                        " join fetch o.delivery d", Order.class
        ).getResultList();
    }
    
    // DTO
    @Data
    class SimpleOrderDto{
        private Long orderId;
        private String name;
        private LocalDateTime orderDate;
        private OrderStatus orderStatus;
        private Address address;

        public SimpleOrderDto(Order order) {
            this.orderId = order.getId();
            this.name = order.getMember().getName();
            this.orderDate = order.getOrderDate();
            this.orderStatus = order.getStatus();
            this.address = order.getDelivery().getAddress();
        }
    }

JPA DTO 바로 조회

성능은 패치조인보다 약간 빠르지만 코드 재활용성을 할 수 없다

    public List<OrderSimpleQueryDto> findOrderDtos() {
        return em.createQuery(
                "select new jpabook.jpashop.repository.OrderSimpleQueryDto(o.id,m.name,o.orderDate,o.status,d.address)" +
                        " from Order o"+
                        " join o.member m" +
                        " join o.delivery d", OrderSimpleQueryDto.class)
                .getResultList();
    }