JPA认为我正在删除一个分离的对象

Question

我有一个DAO，我曾经使用JPA加载和保存我的域对象。我终于设法让交易工作正常，现在我又遇到了另一个问题。

在我的测试用例中，我调用我的DAO来加载具有给定id的域对象，检查它是否已加载，然后调用相同的DAO来删除刚刚加载的对象。当我这样做时，我得到以下内容：

java.lang.IllegalArgumentException: Removing a detached instance mil.navy.ndms.conops.common.model.impl.jpa.Group#10
 at org.hibernate.ejb.event.EJB3DeleteEventListener.performDetachedEntityDeletionCheck(EJB3DeleteEventListener.java:45)
 at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:108)
 at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:74)
 at org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:794)
 at org.hibernate.impl.SessionImpl.delete(SessionImpl.java:772)
 at org.hibernate.ejb.AbstractEntityManagerImpl.remove(AbstractEntityManagerImpl.java:253)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
 at java.lang.reflect.Method.invoke(Method.java:600)
 at org.springframework.orm.jpa.SharedEntityManagerCreator$SharedEntityManagerInvocationHandler.invoke(SharedEntityManagerCreator.java:180)
 at $Proxy27.remove(Unknown Source)
 at mil.navy.ndms.conops.common.dao.impl.jpa.GroupDao.delete(GroupDao.java:499)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
 at java.lang.reflect.Method.invoke(Method.java:600)
 at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:304)
 at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
 at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
 at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
 at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
 at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
 at $Proxy28.delete(Unknown Source)
 at mil.navy.ndms.conops.common.dao.impl.jpa.GroupDaoTest.testGroupDaoSave(GroupDaoTest.java:89)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:48)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:37)
 at java.lang.reflect.Method.invoke(Method.java:600)
 at junit.framework.TestCase.runTest(TestCase.java:164)
 at junit.framework.TestCase.runBare(TestCase.java:130)
 at junit.framework.TestResult$1.protect(TestResult.java:106)
 at junit.framework.TestResult.runProtected(TestResult.java:124)
 at junit.framework.TestResult.run(TestResult.java:109)
 at junit.framework.TestCase.run(TestCase.java:120)
 at junit.framework.TestSuite.runTest(TestSuite.java:230)
 at junit.framework.TestSuite.run(TestSuite.java:225)
 at org.eclipse.jdt.internal.junit.runner.junit3.JUnit3TestReference.run(JUnit3TestReference.java:130)
 at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
 at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:460)
 at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:673)
 at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:386)
 at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:196)

现在假设我正在使用相同的DAO实例，并且我没有更改EntityManagers（除非Spring不这样做而不让我知道），这怎么可能是一个独立的对象？

我的DAO代码如下所示：

public class GenericJPADao<INTFC extends IAddressable, VO extends BaseAddressable> implements IWebDao, IDao<INTFC>, IDaoUtil<INTFC>
{
    private static Logger logger = Logger.getLogger (GenericJPADao.class);

    protected Class<?> voClass;

    @PersistenceContext(unitName = "CONOPS_PU")
    protected EntityManagerFactory emf;

    @PersistenceContext(unitName = "CONOPS_PU")
    protected EntityManager em;

    public GenericJPADao()
    {
        super ( );

        ParameterizedType genericSuperclass = 
                        (ParameterizedType) getClass ( ).getGenericSuperclass ( );
        this.voClass = (Class<?>) genericSuperclass.getActualTypeArguments ( )[1];
    }


    ...


    public void delete (INTFC modelObj, EntityManager em)
    {
        em.remove (modelObj);
    }

    @SuppressWarnings("unchecked")
    public INTFC findById (Long id)
    {
        return ((INTFC) em.find (voClass, id));
    }
}

测试用例代码如下：

IGroup loadedGroup = dao.findById (group.getId ( ));
assertNotNull (loadedGroup);
assertEquals (group.getId ( ), loadedGroup.getId ( ));

dao.delete (loadedGroup); // - This generates the above exception

loadedGroup = dao.findById (group.getId ( ));
assertNull(loadedGroup);

谁能告诉我这里我做错了什么？

Answer 1

我怀疑您在事务之外运行代码，因此find和delete操作发生在单独的持久性上下文中，find实际上返回分离 instance（所以JPA是对的，你是删除一个分离的对象）。

在事务中包装您的查找/删除序列。

更新：在7.3.1. Transaction Persistence Context章节的摘录中：

  

如果在活动事务之外使用具有事务持久性上下文模型的EntityManager，则每个方法调用都会创建新的持久性上下文，执行方法操作并结束持久性上下文。例如，考虑在事务之外使用EntityManager.find方法。 EntityManager将创建临时持久化上下文，执行查找操作，结束持久化上下文，并将分离的结果对象返回给您。具有相同id的第二个调用将返回第二个分离的对象。

Answer 2

public void remove(Object obj){
    em.remove(em.merge(obj));
}

上述代码与zawhtut

提出的代码类似

Answer 3

+1给Pascal Thivent帖子，只是跟进。

    @Transactional
    public void remove(long purchaseId){
        Purchase attached = jpaTemplate.find(Purchase.class,purchaseId);
        jpaTemplate.remove(attached);
    }

Answer 4

使用em.getReference()代替em.find()来获取实例。

例如，尝试：

em.remove(em.getReference(INTFC.class, id)); 

Answer 5

这是我使用的（基于之前的答案）

public void deleteTask(int taskId) {
    Task task = getTask(taskId); //this is a function that returns a task by id
    if (task == null) {
        return;
    }
    EntityManager em = emf.createEntityManager();
    EntityTransaction et = em.getTransaction();
    et.begin();
    em.remove(em.merge(task));
    et.commit();
    em.close();
}

Answer 6

事务确保ACID属性，但不确保实体是附加还是分离。 即使您在同一个交易中运行entityManager.find和entityManager.remove()，也无法保证将附加该实体。因此，在发出entityManager.remove()之前，请检查实体是否已附加，如果未使用enitityManger.merge(entity)附加，则按照以下方式发出entityManager.remove：

@Transactional
 public void delete (long id)
    {
ModelObj modelObj=entityManager.find(ModelObj.class,id);
modelObj=entityManager.contains(modelObj)?modelObj:entityManager.merge(modelObj);
        em.remove (modelObj);
    }

Answer 7

对我来说有效的方法是调用flush，以便按以下示例进行更改：

@PersistanceContext
EntityManager em;

public SomeObject(...parameters){
    repository.save();
    em.flush();
    repository.delete();
}