多对多使用连接表的双向关联，连接表无法自动生成ID
如题 数据库中有Student Course和Score三张表 Score是连接表
三张表分别都有ID字段为主键 使用@GeneratedValue自动生成ID
但是Score只要使用@GeneratedValue存储就会报错 提示Caused by: java.sql.SQLException: Field 'id' doesn't have a default value 需要初始值
不设ID自动生成存储没问题


求大神帮忙指点一下 谢谢 谢谢


[b]错误信息如下[/b]

org.hibernate.exception.GenericJDBCException: could not insert: [com.hibernate.dao.Score]
  at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:140)
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:128)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:63)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2346)
at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2853)
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.hibernate.dao.HibernateTreeTest.testSave1(HibernateTreeTest.java:68)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:46)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:43)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:270)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49)
at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:62)
at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
at org.junit.runners.ParentRunner.access$000(ParentRunner.ja