Java 在JPA或Hibernate中更新多个关系

我有两个

实体

如下所示

@Entity
@Table(name = "USER")
public class User {
    @Id
    private Long id;

    private String name;

    @ManyToMany(fetch = FetchType.LAZY, mappedBy = "groupMemberList")
    @Fetch(FetchMode.SELECT)
    private List<Group> groupList = new ArrayList<>();

    // Getters - Setters
}


@Entity
@Table(name = "GROUP")
public class Group {
    @Id
    private Long id;

    private String name;

    @ManyToMany(fetch = FetchType.LAZY/*, mappedBy = "groupList"*/)
    @Fetch(FetchMode.SELECT)
    @JoinTable(name = "SEC_GROUP_VS_MEMBER", joinColumns = @JoinColumn(name = "GROUP_ID"),
            inverseJoinColumns = @JoinColumn(name = "MEMBER_ID"))
    private List<User> groupMemberList;

    // Getters - Setters
}

方法#2

public boolean updateUser(Long userId, List<Group> groupList) {
    User user = hibernateTemplate.get(User.class, userId);

    user.setGroupList(groupList);
    hibernateTemplate.merge(user); // User not updated with the groups
    return true;
}

public boolean updateUser（长用户标识，列表组列表）{
User User=hibernateTemplate.get（User.class，userId）；
user.setGroupList（groupList）；
hibernateTemplate.merge（user）；//未使用组更新用户
返回true；
}

---

第一种方法很好，但第二种方法不行。但是，当我将

联接表

从

Group.class

移动到

User.class

时，第二种方法工作正常，而不是第一种方法。

问题是

拥有实体

问题

假设

Staff

是

User

的一个子类，那么您的问题是关系中只有一方是所属实体。

mappedBy=“groupMemberList”

使

组

实体成为所属实体，因此仅保留对该实体的更改。这意味着您必须在这两种情况下更新

组

实体中的

组成员列表

。如果您有一个

用户的组列表

，则必须迭代组列表并将

用户

添加到其中。

User

中的

groupList

仅用于检索

给定

用户

和

组成员

实体：

@Entity
public class User {
    @Id @GeneratedValue
    private Long id;

    @ManyToMany(mappedBy = "groupMemberList")
    private List<GroupMember> groupList;

@Entity
public class GroupMember {
    @Id @GeneratedValue
    private Long id;

    @ManyToMany
    private List<User> groupMemberList;

参考：

---

亲爱的@K.Nicholas我可以在两个实体中使用

mappedBy

？如果是这样，会有什么不良影响？@Mr.Mak根据JPA上的所有文档，您将

mappedBy

标记拥有方。显然，一个关系不能有两个拥有方！不，但如果没有映射到的

则实体本身拥有多个关系，但是，如果您有两个多个注释，那么您最终会得到两个单独的关系表，它们映射相同的关系，您可能会疯狂地试图跟踪所有注释，DBA会将您永远列入黑名单，您的经理会称您为天才。见上文参考资料。
@Entity
public class User {
    @Id @GeneratedValue
    private Long id;

    @ManyToMany(mappedBy = "groupMemberList")
    private List<GroupMember> groupList;

@Entity
public class GroupMember {
    @Id @GeneratedValue
    private Long id;

    @ManyToMany
    private List<User> groupMemberList;

// create starting user and membergroup    
tx.begin();
User user = new User();
em.persist(user);
GroupMember group = new GroupMember();
em.persist(group);
tx.commit();
em.clear();

// update users for groupId 2
System.out.println("update users for groupId 2");
tx.begin();
List<User> users = new ArrayList<>();
users.add(user);
group.setGroupMemberList(users);
em.merge(group);            
tx.commit();
em.clear();

// update groups for userId 1 -- doesn't work, not owner of relationship
System.out.println("update groups for userId 1 -- doesn't work, not owner of relationship");
tx.begin();
List<GroupMember> groups = new ArrayList<>();
groups.add(group);
user.setGroupList(groups);
em.merge(user);            
tx.commit();
em.clear();

// update groups for userId 1 -- works
System.out.println("update groups for userId 1 -- works");
tx.begin();
for ( GroupMember groupMember: groups) {
    groupMember.getGroupMemberList().add(user);
    em.merge(groupMember);            
}
tx.commit();
em.clear();

Hibernate: insert into User (id) values (?)
Hibernate: insert into GroupMember (id) values (?)
update users for groupId 2
Hibernate: select groupmembe0_.id as id1_0_0_ from GroupMember groupmembe0_ where groupmembe0_.id=?
Hibernate: select groupmembe0_.groupList_id as groupLis1_1_0_, groupmembe0_.groupMemberList_id as groupMem2_1_0_, user1_.id as id1_4_1_ from GroupMember_User groupmembe0_ inner join User user1_ on groupmembe0_.groupMemberList_id=user1_.id where groupmembe0_.groupList_id=?
Hibernate: select user0_.id as id1_4_0_ from User user0_ where user0_.id=?
Hibernate: insert into GroupMember_User (groupList_id, groupMemberList_id) values (?, ?)
update groups for userId 1 -- doesn't work, not owner of relationship
Hibernate: select user0_.id as id1_4_0_ from User user0_ where user0_.id=?
Hibernate: select groupmembe0_.id as id1_0_0_ from GroupMember groupmembe0_ where groupmembe0_.id=?
update groups for userId 1 -- works
Hibernate: select groupmembe0_.id as id1_0_0_ from GroupMember groupmembe0_ where groupmembe0_.id=?
Hibernate: select groupmembe0_.groupList_id as groupLis1_1_0_, groupmembe0_.groupMemberList_id as groupMem2_1_0_, user1_.id as id1_4_1_ from GroupMember_User groupmembe0_ inner join User user1_ on groupmembe0_.groupMemberList_id=user1_.id where groupmembe0_.groupList_id=?
Hibernate: delete from GroupMember_User where groupList_id=?
Hibernate: insert into GroupMember_User (groupList_id, groupMemberList_id) values (?, ?)
Hibernate: insert into GroupMember_User (groupList_id, groupMemberList_id) values (?, ?)