인프런 커뮤니티 질문&답변

영한님 안녕하세요. 강의를 잘 듣고 있습니다!

학습 중 궁금한 점이 있어 질문 드립니다.

엔티티를 저장할 때에는 연관된 엔티티가 모두 영속 상태여야 한다고 알고 있습니다. 다음 코드에서 현재 user와 연관된 teamB는 영속 상태가 아닙니다. 따라서 실행 시 에러가 발생할 것으로 예상했습니다. 그러나 에러 없이 잘 동작하였고, DB를 확인해 보니 user의 team이 현재 연관된 teamB가 아니라 teamA로 되어 있었습니다.

@Entity
@Table(name="users")
public class User {
    @Id @GeneratedValue
    @Column(name="user_id")
    private Long id;

    private String username;

    @ManyToOne
    @JoinColumn(name="team_id")
    private Team team;


    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Team getTeam() {
        return team;
    }

    public void setTeam(Team team) {
        this.team = team;
    }
}

@Entity
public class Team {
    @Id @GeneratedValue
    @Column(name="team_id")
    private Long id;

    private String teamName;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getTeamName() {
        return teamName;
    }

    public void setTeamName(String teamName) {
        this.teamName = teamName;
    }
}

public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("hello");
        EntityManager em = emf.createEntityManager();
        EntityTransaction tx = em.getTransaction();

        tx.begin();
        try{
            Team teamA = new Team();
            teamA.setTeamName("teamA");

            System.out.println(" =====[1]===== ");
            System.out.println("teamA = " + teamA);
            System.out.println("teamA.getId() = " + teamA.getId());
            System.out.println("teamA.getTeamName() = " + teamA.getTeamName());
            System.out.println(" 영속? = " + em.contains(teamA));
            System.out.println(" ============= ");
            System.out.println();

            em.persist(teamA);

            System.out.println(" =====[2]===== ");
            System.out.println("teamA = " + teamA);
            System.out.println("teamA.getId() = " + teamA.getId());
            System.out.println("teamA.getTeamName() = " + teamA.getTeamName());
            System.out.println(" 영속? = " + em.contains(teamA));
            System.out.println(" ============= ");
            System.out.println();

            Team findMyTeam = em.find(Team.class, teamA.getId());

            System.out.println(" =====[3]===== ");
            System.out.println("findMyTeam = " + findMyTeam);
            System.out.println("findMyTeam.getId() = " + findMyTeam.getId());
            System.out.println("findMyTeam.getTeamName() = " + findMyTeam.getTeamName());
            System.out.println(" 영속? = " + em.contains(findMyTeam));
            System.out.println(" ============= ");
            System.out.println();

            Team teamB = new Team();
            teamB.setId(findMyTeam.getId());
            teamB.setTeamName("teamB");

            System.out.println(" =====[4]===== ");
            System.out.println("teamB = " + teamB);
            System.out.println("teamB.getId() = " + teamB.getId());
            System.out.println("teamB.getTeamName() = " + teamB.getTeamName());
            System.out.println(" 영속? = " + em.contains(teamB));
            System.out.println(" ============= ");
            System.out.println();

            User user = new User();
            user.setUsername("username");
            user.setTeam(teamB);

            System.out.println(" =====[5]===== ");
            System.out.println("user.getTeam() = " + user.getTeam());
            System.out.println("teamB = " + teamB);
            System.out.println("teamB.getId() = " + teamB.getId());
            System.out.println("teamB.getTeamName() = " + teamB.getTeamName());
            System.out.println(" 영속? = " + em.contains(teamB));
            System.out.println(" ============= ");
            System.out.println();

            em.persist(user);

            System.out.println(" =====[6]===== ");
            System.out.println("user.getTeam() = " + user.getTeam());
            System.out.println("teamB = " + teamB);
            System.out.println("teamB.getId() = " + teamB.getId());
            System.out.println("teamB.getTeamName() = " + teamB.getTeamName());
            System.out.println(" 영속? = " + em.contains(teamB));
            System.out.println(" ============= ");
            System.out.println();

            tx.commit();

            System.out.println(" =====[7]===== ");
            System.out.println("user.getTeam() = " + user.getTeam());
            System.out.println("teamB = " + teamB);
            System.out.println("teamB.getId() = " + teamB.getId());
            System.out.println("teamB.getTeamName() = " + teamB.getTeamName());
            System.out.println(" 영속? = " + em.contains(teamB));
            System.out.println(" ============= ");
            System.out.println();

        }catch(Exception e){
            e.printStackTrace();
            tx.rollback();
        }finally{
            em.close();
        }

        emf.close();
    }

 =====[1]===== 
teamA = hellojpa.Team@fa5f81c
teamA.getId() = null
teamA.getTeamName() = teamA
 영속? = false
 ============= 

 =====[2]===== 
teamA = hellojpa.Team@fa5f81c
teamA.getId() = 1
teamA.getTeamName() = teamA
 영속? = true
 ============= 

 =====[3]===== 
findMyTeam = hellojpa.Team@fa5f81c
findMyTeam.getId() = 1
findMyTeam.getTeamName() = teamA
 영속? = true
 ============= 

 =====[4]===== 
teamB = hellojpa.Team@dd4aec3
teamB.getId() = 1
teamB.getTeamName() = teamB
 영속? = false
 ============= 

 =====[5]===== 
user.getTeam() = hellojpa.Team@dd4aec3
teamB = hellojpa.Team@dd4aec3
teamB.getId() = 1
teamB.getTeamName() = teamB
 영속? = false
 ============= 

 =====[6]===== 
user.getTeam() = hellojpa.Team@dd4aec3
teamB = hellojpa.Team@dd4aec3
teamB.getId() = 1
teamB.getTeamName() = teamB
 영속? = false
 ============= 

 =====[7]===== 
user.getTeam() = hellojpa.Team@dd4aec3
teamB = hellojpa.Team@dd4aec3
teamB.getId() = 1
teamB.getTeamName() = teamB
 영속? = false
 ============= 

궁금한 점은 다음과 같습니다:

1. teamB가 영속 상태가 아닌데 어떻게 user가 저장될 수 있었는지 궁금합니다.

2. user는 현재 teamB와 연관되어 있는데, 왜 DB에는 teamA가 나오는지 궁금합니다.

좋은 강의 감사합니다!!