JPA持久化异常：PersistenceException: org.hibernate.PersistentObjectException

1.PersistenceException异常如下

javax.persistence.PersistenceException: org.hibernate.PersistentObjectException: detached entity passed to persist: com.java.bean.Student
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:147)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:155)
at org.hibernate.internal.ExceptionConverterImpl.convert(ExceptionConverterImpl.java:162)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:780)
at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:758)
at com.java.test.Test.testInsertS(Test.java:68)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at junit.framework.TestCase.runTest(TestCase.java:176)
at junit.framework.TestCase.runBare(TestCase.java:141)
at junit.framework.TestResult$1.protect(TestResult.java:122)
at junit.framework.TestResult.runProtected(TestResult.java:142)
at junit.framework.TestResult.run(TestResult.java:125)
at junit.framework.TestCase.run(TestCase.java:129)
at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:131)
at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
Caused by: org.hibernate.PersistentObjectException: detached entity passed to persist: com.java.bean.Student
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:124)
at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:58)
at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:773)
… 18 more

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2.通常出现PersistenceException原因

通常原因都是设置了- -主键自增策略 @GeneratedValue(strategy=GenerationType.IDENTITY)

1-设置主键自增时，必须在数据库中设置主键自增和在对应的实体类中设置对应的主键自增，只要有哪一边没有设置，就会报该异常

2-在设置了主键自增了，保存数据时，自己设置了主键，则也会报PersistenceException

比如Student类中sid为主键，并且设置了主键自增，但是持久化时，new对象时给了id

Student tStudent=new Student(2, "哈哈", 2);//此时会报错，不能设置sid