休眠:LazyInitializationException:无法初始化代理 [英] hibernate: LazyInitializationException: could not initialize proxy

问题描述

这是一个让我感到困惑的地方.我正在尝试实现一个基本的 Hibernate DAO 结构，但遇到了问题.

Here's one that has me perplexed. I'm trying to implement a basic Hibernate DAO structure, but am having a problem.

以下是基本代码:

int startingCount = sfdao.count();
sfdao.create( sf );
SecurityFiling sf2 = sfdao.read( sf.getId() );
sfdao.delete( sf );
int endingCount = sfdao.count();

assertTrue( startingCount == endingCount );
assertTrue( sf.getId().longValue() == sf2.getId().longValue() );
assertTrue( sf.getSfSubmissionType().equals( sf2.getSfSubmissionType() ) );
assertTrue( sf.getSfTransactionNumber().equals( sf2.getSfTransactionNumber() ) );

它在第三个 assertTrue 上失败，它试图将 sf 中的值与 sf2 中的相应值进行比较.这是一个例外:

It fails on the third assertTrue where it's trying to compare a value in sf to the corresponding value in sf2. Here's the exception:

org.hibernate.LazyInitializationException: could not initialize proxy - no Session
    at org.hibernate.proxy.AbstractLazyInitializer.initialize(AbstractLazyInitializer.java:86)
    at org.hibernate.proxy.AbstractLazyInitializer.getImplementation(AbstractLazyInitializer.java:140)
    at org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer.invoke(JavassistLazyInitializer.java:190)
    at com.freightgate.domain.SecurityFiling_$$_javassist_7.getSfSubmissionType(SecurityFiling_$$_javassist_7.java)
    at com.freightgate.dao.SecurityFilingTest.test(SecurityFilingTest.java:73)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:40)

推荐答案

问题是您试图访问 分离.在访问集合到当前会话之前，您需要重新附加对象.你可以通过

The problem is that you are trying to access a collection in an object that is detached. You need to re-attach the object before accessing the collection to the current session. You can do that through

session.update(object);

使用 lazy=false 不是一个好的解决方案，因为您丢弃了休眠的延迟初始化功能.当lazy=false 时，在请求对象的同时将集合加载到内存中.这意味着如果我们有一个包含 1000 个项目的集合，无论我们是否要访问它们，它们都会被加载到内存中.这不好.

Using lazy=false is not a good solution because you are throwing away the Lazy Initialization feature of hibernate. When lazy=false, the collection is loaded in memory at the same time that the object is requested. This means that if we have a collection with 1000 items, they all will be loaded in memory, despite we are going to access them or not. And this is not good.

请阅读这篇文章，其中解释了问题、可能的解决方案以及实施的原因道路.此外，要了解会话和交易，您必须阅读这篇其他文章.

Please read this article where it explains the problem, the possible solutions and why is implemented this way. Also, to understand Sessions and Transactions you must read this other article.

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