예제 도메인 모델과 동작 확인하기.

1. Entity Class

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• Member와 Team은 다대일 연관관계

 

 

2. ERD

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3. Member class

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• xToOne은 기본적으로 fetch type이 EAGER이다.
• 항상 LAZY를 적용하자(지연로딩)

package study.datajpa.entity;

import lombok.*;


import javax.persistence.*;

@Entity
@Getter @Setter
@NoArgsConstructor(access = AccessLevel.PROTECTED)
@ToString(of = {"id", "userName", "age"})
public class Member {

    @Id @GeneratedValue
    @Column(name = "member_id")
    private Long id;

    private String userName;

    private int age;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "team_id")
    private Team team;

    public Member(String userName) {
        this.userName = userName;
    }

    public Member(String userName, int age, Team team) {
        this.userName = userName;
        this.age = age;
        if(team!=null) {
            this.changeTeam(team);
        }
    }

    public void changeUserName(String userName){
        this.userName = userName;
    }

    public void changeTeam(Team team){
        this.setTeam(team);
        team.getMembers().add(this);
    }

}

 

 

4. Team Class

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package study.datajpa.entity;

import lombok.*;

import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;

@Entity
@Getter
@Setter
@NoArgsConstructor(access = AccessLevel.PROTECTED)
@ToString(of = {"id", "name"})
public class Team {

    @Id @GeneratedValue
    @Column(name = "team_id")
    private Long id;

    private String name;

    @OneToMany(mappedBy = "team")
    private List<Member> members = new ArrayList<>();

    public Team(String name) {
        this.name = name;
    }
}

 

 

 

5. Test

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• 지연 로딩을 적용하면 member.getTeam()실행 시
• team 프록시 객체가 초기화 되며 team을 조회하는 쿼리가 나간다.
• 따라서 member를 조회하는 쿼리로 인해 각member에서 team을 조회할 때 쿼리가 매번 나간다.
• fetch join을 사용하면 쿼리 한번에 member와 관련된 team을 모두 한 번에 가져옴.

@SpringBootTest
@Transactional
class MemberTest {

    @PersistenceContext
    private EntityManager em;

    @Test
    public void testEntity(){
        Team teamA = new Team("teamA");
        Team teamB = new Team("teamB");
        em.persist(teamA);
        em.persist(teamB);

        Member member1 = new Member("member1", 10, teamA);
        Member member2 = new Member("member2", 20, teamA);
        Member member3 = new Member("member3", 30, teamB);
        Member member4 = new Member("member4", 40, teamB);

        em.persist(member1);
        em.persist(member2);
        em.persist(member3);
        em.persist(member4);

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

        List<Member> members = em.createQuery(
                "select m from Member m join fetch m.team", Member.class)
                .getResultList();

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

 

 

 

6. Result

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    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 = Member(id=3, userName=member1, age=10)
member.getTeam() = Team(id=1, name=teamA)
member = Member(id=4, userName=member2, age=20)
member.getTeam() = Team(id=1, name=teamA)
member = Member(id=5, userName=member3, age=30)
member.getTeam() = Team(id=2, name=teamB)
member = Member(id=6, userName=member4, age=40)
member.getTeam() = Team(id=2, name=teamB)

 

 

7. GitHub : 210827 Domain model

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GitHub - bsh6463/SpringDataJpa