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프록시와 연관관계

객체그래프 탐색

객체는 객체 그래프로 연관된 객체를 탐색한다.

Entity는 객체가 데이터베이스(RDB)와 매핑되어 있어서 자유롭개 객체를 탐색하는데 제한이 있다.

// order.getMember() → orders 테이블과 member 테이블의 정보를 모두 가져와야 하는상태.

JPA는 프록시객체라는 기술을 사용하여 연관된 객체를 처음부터 데이터베이스에서 조회하지 않고, 실제 사용하는 시점에 조회할 수 있다.

프록시 객체


@Entity
@Table(name = "member")
public class Member extends BaseEntity {
		...

    @OneToMany(mappedBy = "member", fetch = FetchType.LAZY)
    private List<Order> orders = new ArrayList<>(); // proxy

    ...
}


@Entity
@Table(name = "orders")
public class Order extends BaseEntity {
   ...

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "member_id", referencedColumnName = "id")
    private Member member;

    ...
}


@Test
void proxy() {
    EntityManager entityManager = emf.createEntityManager();

    // 회원 조회 -> 회원의 주문 까지 조회
    Member findMember = entityManager.find(Member.class, 1L);

    log.info("orders is loaded : {}", entityManager.getEntityManagerFactory()
            .getPersistenceUnitUtil().isLoaded(findMember.getOrders()));

		log.info("-------");
    log.info("{}" ,findMember.getOrders().get(0).getMemo());
    log.info("orders is loaded : {}", entityManager.getEntityManagerFactory()
						.getPersistenceUnitUtil().isLoaded(findMember.getOrders()));
}

// 실행결과
Hibernate: select member0_.id as id1_1_0_, member0_.created_at as created_2_1_0_, member0_.created_by as created_3_1_0_, member0_.address as address4_1_0_, member0_.age as age5_1_0_, member0_.description as descript6_1_0_, member0_.name as name7_1_0_, member0_.nickName as nickname8_1_0_ from member member0_ where member0_.id=?
2021-09-11 14:11:52.453  INFO 7960 --- [           main] com.kdt.lecture.domain.order.ProxyTest   : orders is loaded : false
2021-09-11 14:11:52.454  INFO 7960 --- [           main] com.kdt.lecture.domain.order.ProxyTest   : -------
Hibernate: select orders0_.member_id as member_i7_3_0_, orders0_.id as id1_3_0_, orders0_.id as id1_3_1_, orders0_.created_at as created_2_3_1_, orders0_.created_by as created_3_3_1_, orders0_.member_id as member_i7_3_1_, orders0_.memo as memo4_3_1_, orders0_.order_datetime as order_da5_3_1_, orders0_.orderStatus as ordersta6_3_1_ from orders orders0_ where orders0_.member_id=?
2021-09-11 14:11:52.459  INFO 7960 --- [           main] com.kdt.lecture.domain.order.ProxyTest   : 부재시 전화주세요.
2021-09-11 14:11:52.459  INFO 7960 --- [           main] com.kdt.lecture.domain.order.ProxyTest   : orders is loaded : true

프록시의 특징

프록시 객체는 처음 사용할 때 한번만 초기화 된다.

프록시 객체가 초기화되면, 프록시 객체를 통해서 실제 엔티티에 접근 할 수 있다.

초기화는 영속성 컨텍스트의 도움을 받아야 가능하다. 따라서 준영속 상태의 프록시를 초기화하면 LazyInitializationException 예외가 발생한다.

지연로딩(LAZY) & 즉시로딩(EAGER)

지연로딩

엔티티를 조회할때, 연관된 엔티티를 함께 조회한다.

즉시로딩

연관된 엔티티를 실제 사용할 때 조회한다.

영속성 전이(CASCADE)

특정 엔티티를 영속 상태로 만들 때, 연관된 엔티티도 함께 영속상태로 만들고 싶을때, 사용한다.


public enum CascadeType {
    ALL,
    PERSIST,
    MERGE,
    REMOVE,
    REFRESH,
    DETACH;

    private CascadeType() {
    }
}

CASCADE의 종류 - ALL : 모두 적용 - PERSIST :영속 - MERGE : 병합 - REMOVE : 삭제 - REFRESH : REFRESH - DETACH : DETACH

고아객체

부모 엔티티와 연관관계가 끊어진 자식 엔티티를 자동으로 삭제하는 기능이다.


@Entity
@Table(name = "member")
public class Member extends BaseEntity {
    ...

    @OneToMany(mappedBy = "member", fetch = FetchType.LAZY, cascade = CascadeType.ALL, orphanRemoval = true)
    private List<Order> orders = new ArrayList<>();

		...
}


@Test
void orphan() {
    EntityManager entityManager = emf.createEntityManager();

    // 회원 조회 -> 회원의 주문 까지 조회
    Member findMember = entityManager.find(Member.class, 1L);
    findMember.getOrders().remove(0); // order를 제거한다. (고아객체)

    EntityTransaction transaction = entityManager.getTransaction();

    transaction.begin();
    transaction.commit();
}

// 실행결과
Hibernate: call next value for hibernate_sequence
Hibernate: insert into orders (created_at, created_by, member_id, memo, order_datetime, orderStatus, id) values (?, ?, ?, ?, ?, ?, ?)
Hibernate: insert into member (created_at, created_by, address, age, description, name, nickName, id) values (?, ?, ?, ?, ?, ?, ?, ?)
Hibernate: update orders set created_at=?, created_by=?, member_id=?, memo=?, order_datetime=?, orderStatus=? where id=?
Hibernate: select member0_.id as id1_1_0_, member0_.created_at as created_2_1_0_, member0_.created_by as created_3_1_0_, member0_.address as address4_1_0_, member0_.age as age5_1_0_, member0_.description as descript6_1_0_, member0_.name as name7_1_0_, member0_.nickName as nickname8_1_0_ from member member0_ where member0_.id=?
Hibernate: select orders0_.member_id as member_i7_3_0_, orders0_.id as id1_3_0_, orders0_.id as id1_3_1_, orders0_.created_at as created_2_3_1_, orders0_.created_by as created_3_3_1_, orders0_.member_id as member_i7_3_1_, orders0_.memo as memo4_3_1_, orders0_.order_datetime as order_da5_3_1_, orders0_.orderStatus as ordersta6_3_1_ from orders orders0_ where orders0_.member_id=?
Hibernate: delete from orders where id=?

GitHub - wckhg89/kdt-jpa at chapter3-2

Contribute to wckhg89/kdt-jpa development by creating an account on GitHub.

https://github.com/wckhg89/kdt-jpa/tree/chapter3-2

SpringBoot Part4 4-4 프록시