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我有一个带有 Hibernate 5 和 Hibernate-Annotations 的 Spring 4.2 web 应用程序。实体看起来不错，现在我有一大堆 DAO 类，以及 JUnit4 测试来测试这些 DAO。

对于我的一些类，我有到父对象的 FK 映射如下：

public class MyDataEntity extends BaseEntity
{
    @Id
    @Column(name = "row_id")
    private long rowId;

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "parent_id")
    private ParentEntity parent;
}

我们可以假设，还有其他基本字段，我们有所有这些字段的 getter/setter，以及 hashCode、equals 和 toString 方法。

在取回 MyDataEntity 的测试中，我收到一条错误消息，例如：

org.hibernate.HibernateException: HHH000142: Javassist Enhancement failed: com.tomholmes.server.model.common.ParentEntity
at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.getProxy(JavassistProxyFactory.java:130)
at org.hibernate.tuple.entity.AbstractEntityTuplizer.createProxy(AbstractEntityTuplizer.java:666)
at org.hibernate.persister.entity.AbstractEntityPersister.createProxy(AbstractEntityPersister.java:4461)
at org.hibernate.event.internal.DefaultLoadEventListener.createProxyIfNecessary(DefaultLoadEventListener.java:336)
at org.hibernate.event.internal.DefaultLoadEventListener.proxyOrLoad(DefaultLoadEventListener.java:257)
at org.hibernate.event.internal.DefaultLoadEventListener.onLoad(DefaultLoadEventListener.java:137)
at org.hibernate.internal.SessionImpl.fireLoad(SessionImpl.java:1129)
at org.hibernate.internal.SessionImpl.internalLoad(SessionImpl.java:1022)
at org.hibernate.type.EntityType.resolveIdentifier(EntityType.java:632)
at org.hibernate.type.EntityType.resolve(EntityType.java:424)
at org.hibernate.engine.internal.TwoPhaseLoad.doInitializeEntity(TwoPhaseLoad.java:154)
at org.hibernate.engine.internal.TwoPhaseLoad.initializeEntity(TwoPhaseLoad.java:128)
at org.hibernate.loader.Loader.initializeEntitiesAndCollections(Loader.java:1132)
at org.hibernate.loader.Loader.processResultSet(Loader.java:992)
at org.hibernate.loader.Loader.doQuery(Loader.java:930)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:336)
at org.hibernate.loader.Loader.doList(Loader.java:2611)
at org.hibernate.loader.Loader.doList(Loader.java:2594)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2423)
at org.hibernate.loader.Loader.list(Loader.java:2418)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:109)
at org.hibernate.internal.SessionImpl.list(SessionImpl.java:1774)
at org.hibernate.internal.CriteriaImpl.list(CriteriaImpl.java:363)
at com.tomholmes.server.dao.common.MyDataDaoImpl.getMyDataListBySubject(MyDataDaoImpl.java:105)
at com.tomholmes.server.dao.common.MyDataDaoTest.testListBySubject(MyDataDaoTest.java:308)
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:497)
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.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:75)
at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:86)
at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:84)
at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:254)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:89)
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.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:70)
at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:193)
at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:86)
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: java.lang.ClassCastException: com.agmednet.server.model.common.TrialEntity_$$_javassist_29 cannot be cast to javassist.util.proxy.Proxy
at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.getProxy(JavassistProxyFactory.java:123)
... 53 more

解决此问题的简单方法是将 FetchType 从 LAZY 更改为 EAGER，然后错误消息就会消失。

我知道我以前对此做过一些研究，但我不记得我发现了什么。通常，当我从数据库中获取对象时，我会获取该对象，将其转换为 JSON 并将其发送到前端。我可能并不总是需要 ParentEntity 记录。如果我从后端的“MyData”获取记录，并且我计划稍后获取父项，那么我应该能够延迟加载它。

我的老板，宁愿我做延迟加载，我可以理解当我们不需要时不获取大对象，但我需要避免出现这个错误，所以也许我只需要调整我的配置以使延迟 -装载工作。或者，如果我不能使用延迟加载，那么我只需要一个我可以解释的理由。

谢谢您的帮助！

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