Member 엔티티

package study.datajpa.entity;

import jakarta.persistence.*;
import lombok.*;

@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){
            changeTeam(team);
        }
    }

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

• 롬복 설명
  • @Setter: 실무에서 가급적 Setter는 사용하지 않기
  • @NoArgsConstructor AccessLevel.PROTECTED: 기본 생성자 막고 싶은데, JPA 스팩상 PROTECTED로 열어두어야 함
  • @ToString은 가급적 내부 필드만(연관관계 없는 필드만)
• changeTeam() 으로 양방향 연관관계 한번에 처리(연관관계 편의 메소드)

Team 엔티티

package study.datajpa.entity;

import jakarta.persistence.*;
import lombok.*;

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;
    }
}

• Member와 Team은 양방향 연관관계, Member.team 이 연관관계의 주인, Team.members 는 연관관계의 주인이 아님, 따라서 Member.team 이 데이터베이스 외래키 값을 변경, 반대편은 읽기만 가능

MemberTest

package study.datajpa.entity;

import jakarta.persistence.EntityManager;
import jakarta.persistence.PersistenceContext;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.annotation.Rollback;
import org.springframework.transaction.annotation.Transactional;

import java.util.List;

import static org.junit.jupiter.api.Assertions.*;

@SpringBootTest
@Transactional
@Rollback(value = false)
class MemberTest {
    @PersistenceContext
    EntityManager em;

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

        Member membe1 = new Member("membe1", 10, teamA);
        Member membe2 = new Member("membe2", 20, teamA);
        Member membe3 = new Member("membe3", 30, teamB);
        Member membe4 = new Member("membe4", 40, teamB);

        em.persist(membe1);
        em.persist(membe2);
        em.persist(membe3);
        em.persist(membe4);

        // 초기화
        em.flush(); // 강제로 DB에 insert 쿼리 날림
        em.clear(); // DB 쿼리 날리고 JPA 영속성 컨텍스트의 캐시를 다 날림

        //확인
        List<Member> members = em.createQuery("select m from Member m", Member.class).getResultList();

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

    }
}

가급적 순수 JPA로 동작 확인 (뒤에서 변경) db 테이블 결과 확인 지연 로딩 동작 확인