지연 로딩과 조회 성능 최적화(FETCH JOIN)

FETCH JOIN

Fetch Join2

 

 

1. Fetch Join을 활용

 public List<Order> findAllWithMemberDelivery() {

       return  em.createQuery("select o from Order o " +
                "join fetch o.member " +
                "join fetch o.delivery", Order.class).getResultList();
    }

 

• join fetch 를 통해 order를 가져오는 쿼리 한 번에 member와 delibery도 함께 조회한다.

 

 

  @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;
    }

• 와! 쿼리 한번으로 끝났다.

Hibernate: 
    select
        order0_.order_id as order_id1_6_0_,
        member1_.member_id as member_i1_4_1_,
        delivery2_.delivery_id as delivery1_2_2_,
        order0_.delivery_id as delivery4_6_0_,
        order0_.member_id as member_i5_6_0_,
        order0_.order_date as order_da2_6_0_,
        order0_.status as status3_6_0_,
        member1_.city as city2_4_1_,
        member1_.street as street3_4_1_,
        member1_.zipcode as zipcode4_4_1_,
        member1_.name as name5_4_1_,
        delivery2_.city as city2_2_2_,
        delivery2_.street as street3_2_2_,
        delivery2_.zipcode as zipcode4_2_2_,
        delivery2_.status as status5_2_2_ 
    from
        orders order0_ 
    inner join
        member member1_ 
            on order0_.member_id=member1_.member_id 
    inner join
        delivery delivery2_ 
            on order0_.delivery_id=delivery2_.delivery_id

 

2. 정리

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• 엔티티를 fetch join을 사용하여 쿼리 한 번으로 모두 조회함
• 페치 조인으로 인해 order -> member, order -> delivery 는 이미 조회된 상태로 지연로딩 적용될 필요 없음.

 

 

3. GitHiub : 210822 FETCH JOIN

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GitHub - bsh6463/SpringBootJPA1