detached entity passed to persist 错误的引起的原因和解决办法

今天在测试整合Spring和Hibernate的时候，遇到了一个问题，报错情况如下：

报错信息：

org.springframework.dao.InvalidDataAccessApiUsageException: detached entity passed to persist: com.bean.Cat; nested exception is org.hibernate.PersistentObjectException: detached entity passed to persist: com.bean.Cat    at org.springframework.orm.hibernate3.SessionFactoryUtils.convertHibernateAccessException(SessionFactoryUtils.java:668)    at org.springframework.orm.hibernate3.HibernateAccessor.convertHibernateAccessException(HibernateAccessor.java:412)    at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:411)    at org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)    at org.springframework.orm.hibernate3.HibernateTemplate.persist(HibernateTemplate.java:793)    at com.dao.impl.CatDaoImpl.createCat(CatDaoImpl.java:20)    at com.test.TestCat.testAdd(TestCat.java:35)    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.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)    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: org.hibernate.PersistentObjectException: detached entity passed to persist: com.bean.Cat    at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:127)    at org.hibernate.event.def.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:61)    at org.hibernate.impl.SessionImpl.firePersist(SessionImpl.java:808)    at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:782)    at org.hibernate.impl.SessionImpl.persist(SessionImpl.java:786)    at org.springframework.orm.hibernate3.HibernateTemplate$21.doInHibernate(HibernateTemplate.java:796)    at org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:406)    ... 29 more

报错原因：

从报错信息“detached entity passed to persist: com.bean.Cat”可以分析出，该错误是在Cat持久化转换时出的错。下面是测试的部分代码：

Cat实体类

/** * @Author: zsh * @Title: Cat.java * @Description:Cat实体类 * @Date:2016年9月18日 下午3:12:23 */@Entity@Table(name = "cat")public class Cat {    @Id    @GeneratedValue(strategy = GenerationType.AUTO)    private Integer id;    @Column(name = "name")    private String name;    @Temporal(value = TemporalType.TIMESTAMP)    private Date createDate;    ……省略了构造器及setter、getter方法。

注意：使用注解的时候，为了避免破坏Java的封装特性，一般会写在get方法上，此处为了方便分析，所以写在字段上方。

测试方法

@Test    public void testAdd() throws ParseException{        Cat cat = new Cat(2,"TOM",new SimpleDateFormat("yyyy-MM-dd").parse("2000-1-1"));        cDao.createCat(cat);    }

通过分析两段代码可以发现，在实体类中设置了ID字段的自增，但是在测试时，实例化Cat类的时候又指定了ID的值，所以在运行的时候会报出错误！

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解决方法：

1、取消字段自增设置
2、实例化Cat对象时不设置ID值