실전! 스프링 부트와 JPA 활용2: API 개발 고급 - 지연 로딩과 조회 성능 최적화

package jpabook.jpashop.api;
/**
 * xToOne(ManyToOne, OneToOne) - 성능 최적화
 * Order
 * Order -> Member
 * Order -> Delivery
 */
@RestController
@RequiredArgsConstructor
public class OrderSimpleApiController {

    private final OrderRepository orderRepository;

    /**
     * V1. 엔티티 직접 노출
     * - Hibernate5Module 모듈 등록, LAZY=null 처리 * - 양방향 관계 문제 발생 -> @JsonIgnore
     */
    
    @GetMapping("/api/v1/simple-orders")
    public List<Order> ordersV1() {
        List<Order> all = orderRepository.findAllByString(new OrderSearch());
        for (Order order : all) {
            order.getMember().getName();
            order.getDelivery().getAddress();
        }
        return all;
    }
}

@SpringBootApplication
public class JpashopApplication {

	public static void main(String[] args) {
		SpringApplication.run(JpashopApplication.class, args);
	}

	@Bean
	Hibernate5Module hibernate5Module() {
		Hibernate5Module hibernate5Module = new Hibernate5Module();
		//강제 지연 로딩 설정 (사실 아래에 있는 건 쓰면 안됨)
		hibernate5Module.configure(Hibernate5Module.Feature.FORCE_LAZY_LOADING,true);
		return hibernate5Module;
	}
}

package jpabook.jpashop.api;

@RestController
@RequiredArgsConstructor
public class OrderSimpleApiController {

    private final OrderRepository orderRepository;

    @GetMapping("/api/v2/simple-orders")
    public List<SimpleOrderDto> ordersV2() {
        // ORDER 2개
        // N + 1 -> 1 + N(2): 첫번째 쿼리의 결과로 n번만큼 query가 추가 실행되는 게 N + 1이라는 의미임.
        // N + 1 -> 1 + 회원 N + 배송 N
        List<Order> orders = orderRepository.findAllByString(new OrderSearch());

        List<SimpleOrderDto> result = orders
                .stream()
                .map(o -> new SimpleOrderDto(o))
                .collect(Collectors.toList());

        return result;
    }

    @Data
    static class SimpleOrderDto {
        private Long orderId;
        private String name;
        private LocalDateTime orderDate;
        private OrderStatus orderStatus;
        private Address address;

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

package jpabook.jpashop.api;

@RestController
@RequiredArgsConstructor
public class OrderSimpleApiController {

    private final OrderRepository orderRepository;

    @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;
    }
}

@Repository
@RequiredArgsConstructor
public class OrderRepository {

    private final EntityManager em;

    // 재사용성 O
    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();
    }
}

@RestController
@RequiredArgsConstructor
public class OrderSimpleApiController {

    private final OrderRepository orderRepository;
    private final OrderSimpleQueryRepository orderSimpleQueryRepository; // 의존관계 주입(V4)

    @GetMapping("/api/v4/simple-orders")
    public List<OrderSimpleQueryDto> ordersV4() {
        return orderSimpleQueryRepository.findOrderDto();
    }
}

package jpabook.jpashop.repository.order.simplequery;

/**
 * 성능 최적화 관련 레포지토리 경우
 * 따로 패키지를 만들어서 그 안에 관련 클래스를 만든다.
 */
@Repository
@RequiredArgsConstructor
public class OrderSimpleQueryRepository {

    private final EntityManager em;

    // 재사용 X, 유지보수성 O
    // 이런 식으로 성능 최적화에 대한 것은 따로 패키지를 분리하는 것을 권장함
    public List<OrderSimpleQueryDto> findOrderDto() {
        return em.createQuery(
                        "select new jpabook.jpashop.repository.order.simplequery.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();
    }
}

package jpabook.jpashop.repository.order.simplequery;

@Data
public class OrderSimpleQueryDto {
    private Long orderId;
    private String name;
    private LocalDateTime orderDate;
    private OrderStatus orderStatus;
    private Address address;

    public OrderSimpleQueryDto(Long orderId, String name, LocalDateTime orderDate, OrderStatus orderStatus, Address address) {
        this. orderId = orderId;
        this.name = name;
        this.orderDate = orderDate;
        this.orderStatus = orderStatus;
        this.address = address;
    }
}