@EntityGraph

1. @EntityGraph?

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• 연관된 엔티티들을 SQL 한번에 조회하는방법

 

 

2. 사례

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• member -> team은 다대일 지연로딩 관계.
• 따라서 team에 대한 데이터 접근(team.get~) 시 쿼리가 날라감.
• 따라서 member에 대한 쿼리 외에 team의 데이터 조회하는 쿼리 나감.
• 즉 N+1 이슈 발생함.

 

 

 

3. member만 조회

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@Test
    public void findMemberLazy(){
        //given
        //member1 -> TeamA
        //member2 -> TeamB

        Team teamA = new Team("teamA");
        Team teamB = new Team("teamB");
        teamRepository.save(teamA);
        teamRepository.save(teamB);

        Member member1 = new Member("member1", 10, teamA);
        Member member2 = new Member("member2", 10, teamB);
        memberRepository.save(member1);
        memberRepository.save(member2);

        em.flush();
        em.clear();

        //when
        List<Member> members = memberRepository.findAll();

        System.out.println("===================");
        for (Member member : members) {
            System.out.println("member.getUserName() = " + member.getUserName());
        }
    }

멤버 조회하는 쿼리만 날라감.

    select
        member0_.member_id as member_i1_0_,
        member0_.age as age2_0_,
        member0_.team_id as team_id4_0_,
        member0_.user_name as user_nam3_0_ 
    from
        member member0_

===================
member.getUserName() = member1
member.getUserName() = member2

 

 

 

4. member의 팀이름 조회

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• member.getTeam().getName()
• 지연로딩 이므로 team.getName()실행 시 프록시 초기화됨.
• 이 때  team을 조회하는 쿼리 날라감.
• N+1!!!

@Test
    public void findMemberLazy(){
        //given
        //member1 -> TeamA
        //member2 -> TeamB

        Team teamA = new Team("teamA");
        Team teamB = new Team("teamB");
        teamRepository.save(teamA);
        teamRepository.save(teamB);

        Member member1 = new Member("member1", 10, teamA);
        Member member2 = new Member("member2", 10, teamB);
        memberRepository.save(member1);
        memberRepository.save(member2);

        em.flush();
        em.clear();

        //when
        List<Member> members = memberRepository.findAll();

        System.out.println("===================");
        for (Member member : members) {
            System.out.println("member.getUserName() = " + member.getUserName());
            System.out.println("member.getTeam().getName() = " + member.getTeam().getName());
        }
    }

    select
        member0_.member_id as member_i1_0_,
        member0_.age as age2_0_,
        member0_.team_id as team_id4_0_,
        member0_.user_name as user_nam3_0_ 
    from
        member member0_

===================
member.getUserName() = member1
                    
    select
        team0_.team_id as team_id1_1_0_,
        team0_.name as name2_1_0_ 
    from
        team team0_ 
    where
        team0_.team_id=?


member.getUserName() = member2
 
    select
        team0_.team_id as team_id1_1_0_,
        team0_.name as name2_1_0_ 
    from
        team team0_ 
    where
        team0_.team_id=?

 

 

 

 

5. fetch join 사용

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@Query("select m from Member m join fetch m.team t")
List<Member> findMemberFetchJoin();

   @Test
    public void findMemberLazy(){
        //given
        //member1 -> TeamA
        //member2 -> TeamB

        Team teamA = new Team("teamA");
        Team teamB = new Team("teamB");
        teamRepository.save(teamA);
        teamRepository.save(teamB);

        Member member1 = new Member("member1", 10, teamA);
        Member member2 = new Member("member2", 10, teamB);
        memberRepository.save(member1);
        memberRepository.save(member2);

        em.flush();
        em.clear();

        //when
        List<Member> members = memberRepository.findMemberFetchJoin();

        System.out.println("===================");
        for (Member member : members) {
            System.out.println("member.getUserName() = " + member.getUserName());
            System.out.println("member.getTeam().getName() = " + member.getTeam().getName());
            System.out.println("member.getTeam().getClass() = " + member.getTeam().getClass());
        }
    }

• fetch join을 사용하면 member조회시 연관엔티티인 team도 모두 조회하여
• team엔티티 생성해서 Team에 넣어둠. 프록시 객체가 아님.

    select
        member0_.member_id as member_i1_0_0_,
        team1_.team_id as team_id1_1_1_,
        member0_.age as age2_0_0_,
        member0_.team_id as team_id4_0_0_,
        member0_.user_name as user_nam3_0_0_,
        team1_.name as name2_1_1_ 
    from
        member member0_ 
    inner join
        team team1_ 
            on member0_.team_id=team1_.team_id

===================
member.getUserName() = member1
member.getTeam().getName() = teamA
member.getTeam().getClass() = class study.datajpa.entity.Team
member.getUserName() = member2
member.getTeam().getName() = teamB
member.getTeam().getClass() = class study.datajpa.entity.Team

 

 

 

6. 문제점, 방법

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• 근데 SpringDataJpa는 매번 @Query를 사용하는게 아닌데:?
• 그럼 fetch join  어떻게 적용하지?
• @EntityGraph -> fetch join 적용 가능. 어떤 엔티티에 적용할지 정해줘야함.
  • attributePath = {""} -> You can refer to direct properties of the entity or nested properties via a property.nestedProperty.
  • 기본적으로 left outer join임

@Override
@EntityGraph(attributePaths = {"team"})
List<Member> findAll();

   @Test
    public void findMemberLazy(){
        //given
        //member1 -> TeamA
        //member2 -> TeamB

        Team teamA = new Team("teamA");
        Team teamB = new Team("teamB");
        teamRepository.save(teamA);
        teamRepository.save(teamB);

        Member member1 = new Member("member1", 10, teamA);
        Member member2 = new Member("member2", 10, teamB);
        memberRepository.save(member1);
        memberRepository.save(member2);

        em.flush();
        em.clear();

        //when
        List<Member> members = memberRepository.findAll();

        System.out.println("===================");
        for (Member member : members) {
            System.out.println("member.getUserName() = " + member.getUserName());
            System.out.println("member.getTeam().getName() = " + member.getTeam().getName());
            System.out.println("member.getTeam().getClass() = " + member.getTeam().getClass());
        }
    }

    select
        member0_.member_id as member_i1_0_0_,
        team1_.team_id as team_id1_1_1_,
        member0_.age as age2_0_0_,
        member0_.team_id as team_id4_0_0_,
        member0_.user_name as user_nam3_0_0_,
        team1_.name as name2_1_1_ 
    from
        member member0_ 
    left outer join
        team team1_ 
            on member0_.team_id=team1_.team_id

===================
member.getUserName() = member1
member.getTeam().getName() = teamA
member.getTeam().getClass() = class study.datajpa.entity.Team
member.getUserName() = member2
member.getTeam().getName() = teamB
member.getTeam().getClass() = class study.datajpa.entity.Team

• @Query, @EntityGraph같이 사용 가능

@EntityGraph(attributePaths = {"team"})
@Query("select m from Member m")
List<Member> findMemberEntityGraph();

 

 

8. NamedGraph

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• Member Class에 @NamedEntityGraph 사용 가능
• @NamedAttributeNode(("엔티티 이름"))

@NamedEntityGraph(name = "Member.all", attributeNodes =
@NamedAttributeNode("team"))
@Entity
public class Member {}

• 사용방법
• @EntityGraph("name")

@EntityGraph("Member.all")
@Query("select m from Member m")
List<Member> findMemberEntityGraph();

 

 

8. GitHub : 210829 @EntityGraph

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GitHub - bsh6463/SpringDataJpa