Java 使用联接表休眠多对多级联存储

如果可能的话，这就是我想要实现的目标。 我正在尝试使用级联将以下对象保存到DB中

这是我遇到的问题的一个简化示例。我认为它的工作方式是hibernate应该按顺序插入“User”然后是“Group”然后是“UserGroup”，但实际情况是，它先插入“User”然后是“UserGroup”，这会导致下面日志中的组出现“对象引用未保存的临时实例”错误

显然，用它们自己的save（）调用保存单个对象是可行的，但实际的数据库要比这个大得多，我宁愿避免这样做

下面的“TestCode”复制了数据是如何从JSON数据反序列化的

我怀疑这与我的映射有关，但我无法查明原因

作为参考，我使用Hibernate 5.2.10.Final

那么我错过了什么

User.java

@Entity
@Table(name = "User")
public class User implements java.io.Serializable {

private static final long serialVersionUID = -7899020279254796671L;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "userID", unique = true, nullable = false)
private int userId;

@Column(name = "name", nullable = false, length = 45)
private String name;

@OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL,mappedBy = "id.user")
private Set<UserGroup> userGroups = new HashSet<UserGroup>(0);
//Getters, setters, etc...
}

UserGroupdId.java

@Embeddable
public class UserGroupId implements java.io.Serializable {

private static final long serialVersionUID = -3806643465171954306L;

@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@JoinColumn(name = "groupID", nullable = false, insertable = false, updatable = false)
private Group group;

@ManyToOne(fetch = FetchType.LAZY, cascade = CascadeType.ALL)
@JoinColumn(name = "userID", nullable = false, insertable = false, updatable = false)
private User user;
}

测试代码

User u = new User();
u.setName("User");

Group g = new Group();
g.setName("Group");


UserGroup ug = new UserGroup();
UserGroupId id = new UserGroupId();
ug.setId(id);
ug.getId().setGroup(g);
ug.getId().setUser(u);

ug.setDefaultGroup(false);
u.getUserGroups().add(ug);


session.saveOrUpdate(u);

日志条目

[DEBUG] 2017-08-03 10:19:43.497 [main] SQL - insert into M2M.User (name) values (?)
[DEBUG] 2017-08-03 10:19:43.497 [main] SQL - insert into M2M.User (name) values (?)
[TRACE] 2017-08-03 10:19:43.510 [main] BasicBinder - binding parameter [1] as [VARCHAR] - [User]
[TRACE] 2017-08-03 10:19:43.510 [main] BasicBinder - binding parameter [1] as [VARCHAR] - [User]
[DEBUG] 2017-08-03 10:19:43.541 [main] IdentifierGeneratorHelper - Natively generated identity: 65
[DEBUG] 2017-08-03 10:19:43.541 [main] ResourceRegistryStandardImpl - HHH000387: ResultSet's statement was not registered
[DEBUG] 2017-08-03 10:19:43.546 [main] SQL - select usergroup_.groupID, usergroup_.userID, usergroup_.defaultGroup as defaultG1_2_ from M2M.UserGroup usergroup_ where usergroup_.groupID=? and usergroup_.userID=?
[DEBUG] 2017-08-03 10:19:43.546 [main] SQL - select usergroup_.groupID, usergroup_.userID, usergroup_.defaultGroup as defaultG1_2_ from M2M.UserGroup usergroup_ where usergroup_.groupID=? and usergroup_.userID=?
[ERROR] 2017-08-03 10:19:43.546 [main] M2MTest - org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance beforeQuery flushing: m2m.Group

---

从关联中级联是没有意义的

此外，对多对多关联级联

REMOVE

操作也没有意义，因为两个映射实体都是父实体，而联接表是此关联中的子实体

因此，您有两个选择：

如果要映射，需要分别保存

用户

和

组

，并在设置关联双方时级联到

用户组

您可以跳过对联接表的映射，级联将按预期工作。但是，在映射集合关联时，请确保使用列表而不是

列表

User u = new User();
u.setName("User");

Group g = new Group();
g.setName("Group");


UserGroup ug = new UserGroup();
UserGroupId id = new UserGroupId();
ug.setId(id);
ug.getId().setGroup(g);
ug.getId().setUser(u);

ug.setDefaultGroup(false);
u.getUserGroups().add(ug);


session.saveOrUpdate(u);

[DEBUG] 2017-08-03 10:19:43.497 [main] SQL - insert into M2M.User (name) values (?)
[DEBUG] 2017-08-03 10:19:43.497 [main] SQL - insert into M2M.User (name) values (?)
[TRACE] 2017-08-03 10:19:43.510 [main] BasicBinder - binding parameter [1] as [VARCHAR] - [User]
[TRACE] 2017-08-03 10:19:43.510 [main] BasicBinder - binding parameter [1] as [VARCHAR] - [User]
[DEBUG] 2017-08-03 10:19:43.541 [main] IdentifierGeneratorHelper - Natively generated identity: 65
[DEBUG] 2017-08-03 10:19:43.541 [main] ResourceRegistryStandardImpl - HHH000387: ResultSet's statement was not registered
[DEBUG] 2017-08-03 10:19:43.546 [main] SQL - select usergroup_.groupID, usergroup_.userID, usergroup_.defaultGroup as defaultG1_2_ from M2M.UserGroup usergroup_ where usergroup_.groupID=? and usergroup_.userID=?
[DEBUG] 2017-08-03 10:19:43.546 [main] SQL - select usergroup_.groupID, usergroup_.userID, usergroup_.defaultGroup as defaultG1_2_ from M2M.UserGroup usergroup_ where usergroup_.groupID=? and usergroup_.userID=?
[ERROR] 2017-08-03 10:19:43.546 [main] M2MTest - org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance beforeQuery flushing: m2m.Group