Question

我有亲子关系：

@Entity
@Table(name = "user")
public final class User
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Integer userID;

    @Column(name = "username")
    private String userName;

    @OneToMany(cascade = CascadeType.ALL, mappedBy = "admin")
    private Set<News> news;
}

@Entity
@Table(name = "news")
public final class News
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int newsID;

    @ManyToOne(cascade = CascadeType.PERSIST)
    @JoinColumn(name = "userID")
    private User admin;

    @Column(name = "newsText")
    private String newsText;

    @Column(name = "dateOfPost")
    private Date dateOfPost;
}

此处User是父级，News是孩子。我进行级联操作的原因是因为我希望在删除/保留相应的News时删除/保留所有User个对象。此外，当我保留News对象时，我希望保留相应的User [但如果删除News则不删除]。我有一个保存News对象的服务方法，如下所示：

User u = new User("administrator");
News n = new News("News text");
n.setUser(u);       
u.addNews(n);

session.save(n);

对于上面的代码，我得到以下异常：

org.hibernate.exception.ConstraintViolationException: could not insert: [com.maximus.db.model.News]
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:96)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
    at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:64)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2345)
    at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2852)
    at org.hibernate.action.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:71)
    at org.hibernate.engine.ActionQueue.execute(ActionQueue.java:273)
    at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:320)
    at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:203)
    at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:129)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)
    at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)
    at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)
    at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)
    at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:713)
    at org.hibernate.impl.SessionImpl.save(SessionImpl.java:701)
    at org.hibernate.impl.SessionImpl.save(SessionImpl.java:697)
    at com.maximus.db.dao.NewsDAOImpl.addNews(NewsDAOImpl.java:17)
    at com.maximus.db.service.NewsServiceImpl.addNews(NewsServiceImpl.java:31)
    at com.maximus.test.db.service.NewsServiceTest.testAddNewsWithNewUser(NewsServiceTest.java:36)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at org.junit.internal.runners.TestMethodRunner.executeMethodBody(TestMethodRunner.java:99)
    at org.junit.internal.runners.TestMethodRunner.runUnprotected(TestMethodRunner.java:81)
    at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
    at org.junit.internal.runners.TestMethodRunner.runMethod(TestMethodRunner.java:75)
    at org.junit.internal.runners.TestMethodRunner.run(TestMethodRunner.java:45)
    at org.junit.internal.runners.TestClassMethodsRunner.invokeTestMethod(TestClassMethodsRunner.java:66)
    at org.junit.internal.runners.TestClassMethodsRunner.run(TestClassMethodsRunner.java:35)
    at org.junit.internal.runners.TestClassRunner$1.runUnprotected(TestClassRunner.java:42)
    at org.junit.internal.runners.BeforeAndAfterRunner.runProtected(BeforeAndAfterRunner.java:34)
    at org.junit.internal.runners.TestClassRunner.run(TestClassRunner.java:52)
    at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
    at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
    at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'userId' cannot be null
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
    at com.mysql.jdbc.Util.getInstance(Util.java:384)
    at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3566)
    at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3498)
    at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1959)
    at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2113)
    at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2568)
    at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2113)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2409)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2327)
    at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2312)
    at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:94)
    at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:57)
    ... 38 more

这可能是什么问题？

我是否因为尝试保存孩子的服务方法不正确？我应该总是保存父母吗？

感谢。

更新：如果我将用户保存为session.save(u)而不是新闻，一切都很好。那么剩下的问题是，保存孩子而不是父母是不正确的？如果没有，那我该如何实现呢？

Answer 1

你必须做以下事情。这些是： -

从新闻方面删除级联选项。
在您的用例中，您有全新的新闻和新用户。为什么想要坚持新闻。持久化用户对象。两者都将坚持下去。
在您拥有现有用户且想要添加的另一个用例中一个新的新闻。在service / dao实现中创建一个方法用于持久化新闻对象传递用户ID。然后你可以使用加载/获取关联使用并保留新闻项目

Answer 2

我相信你不需要在儿童方面设置级联。只需在父级（User.news）上使用Cascade.ALL即可。

还有一件事，如果你要在删除用户时删除新闻（正如你在帖子中提到的那样），我相信你也需要在父方面添加级联类型Delete Orphan。

休眠：在保存Child之前自动保存Parent

2 个答案: