java - 如何在 Hibernate 中的集合之间移动项目

Question

我在我的应用程序中映射了两个实体，以便为 Team 及其 Members 建模。一个 Team 可以有很多 Members 并且一个 Member 只能属于一个 Team。处理这个概念一切都很好。当我尝试将一个 Member 从一个现有的 Team 移动到另一个时，问题就来了。

实体在下面以简化形式呈现。最后一个方法，transfer()，应该从其 Team 中删除某个 Member 并将其发送给另一个一。

@Entity
public class Member extends Person {
    @ManyToOne
    private Team team;

    protected Member() {
        super();
    }

    public Member(Team team, String name) {
        super(name);
        this.team = team;
    }

    // Trivial getters and setters...

    public Team getTeam() {
        return team;
    }

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

@Entity
public class Team {
    @Id
    private long id;
    private String name;
    @OneToMany(mappedBy="team", cascade=CascadeType.ALL)
    private List<Member> members = new ArrayList<Member>();

    protected Team() {
    }

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

    // trivial getters and setters...

    public Member addMember(String name) {
        Member member = new Member(this, name); 
        members.add(member);
        return member;
    }

    protected void addMember(Member member) {
        members.add(member);
        member.setTeam(this);
    }

    public void removeMember(Member member) {
        members.remove(member);
    }

    public Member memberByName(String memberName) {
        for(Member member : members)
          if(member.getName().equals(memberName))
              return member;
        return null;
    }

    public Collection<Members> getMembers() {
        return Collections.unmodifiableCollection(members);
    }

    public void transfer(Member member, Team destination) {
        members.remove(member);
        destination.addMember(member);
    }
}

我有这个用于验证传输服务的单元测试代码

Team teamA = teamRepository.teamById(idTeamA);
Team teamB = teamRepository.teamById(idTeamB);
Team teamC = teamRepository.teamById(idTeamC);

Member zaki = teamA.memberByName("Zaki");
Member denise = teamA.memberByName("Denise");

EntityTransaction t = teamRepository.transactionBegin();
teamA.transfer(zaki, teamB);
teamA.transferir(denise, teamC);
t.commit();

我在 commit() 行中有以下异常

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: application.domain.Member

有什么想法吗？

更新 1:

我决定进行一些测试，并将 transfer() 方法的代码更改如下

public void transfer(Member member, Team destination) {
    member.setTeam(this);
}

结果很奇怪:没有错误，但也没有对表进行更新。 Hibernate 无法跟踪更新，传输根本就没有发生。

更新 2:

我决定尝试一下来自 Steve K 的建议并将 transfer() 方法更改为以下内容:

    public void transfer(Member member, Team destination) {
        destination.addMember(member);
        members.remove(member);
    }

查看 addMember() 和 removeMember() 方法(如下)，我们看到 Team 也开始更新。

    protected void addMember(Member member) {
        members.add(member);
        member.setTeam(this);
    }

    public void removeMember(Member member) {
        members.remove(member);
    }

因此，成员被添加到目标集合，其团队被设置为目标 Team，然后成员被从当前集合中删除(当前 Team).

测试用例改为

EntityTransaction t = teamRepository.transactionBegin();
teamA.transfer(zaki, teamB);
teamA.getEntityManager().refresh(teamA); // I get an exception here!!!
t.commit();

在 refresh() 行我有以下异常:

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: domain.Member
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1763)
        // ... many calls
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: domain.Member
    at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:139)
        // ... many calls
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.flush(AbstractEntityManagerImpl.java:1335)
    ... 28 more

毕竟，Hibernate 不支持将实例从一个集合转移到另一个集合(实现简单聚合)!

Answer 1

您的映射和数据访问逻辑都很好。

需要在代码开头移动事务边界:

EntityTransaction t = teamRepository.transactionBegin();

Team teamA = teamRepository.teamById(idTeamA);
...
teamA.transferir(denise, teamC);
t.commit();

但是您得到的异常不是来自您向我们展示的代码:

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: application.domain.Member

可能有一个挂起的持久操作正在排队并且只有 translated during flush时间(在你的情况下提交时间)。所以你需要 activate the SQL logs被执行并尝试找出分离的实体。