JPA - 延迟加载 - LazyInitializationException - 不访问子集合时答案

【问题标题】：JPA - Lazy Loading - LazyInitializationException - When Not accessing child collectionJPA - 延迟加载 - LazyInitializationException - 不访问子集合时
【发布时间】：2010-08-06 05:54:55
【问题描述】：

我正在使用 Stripes、Spring、JPA 和 Hibernate 构建一个项目，并且有一个包含多对一子集合的对象。我已将加载设置为懒惰例如。

@OneToMany(cascade = CascadeType.MERGE, mappedBy = "paperOffering", fetch = FetchType.LAZY)
private List<PaperOfferingAssessment> paperOfferingAssessments;

现在，当我从数据库中获取这些对象的集合时，我得到了 LazyInitializationException，即使我在任何阶段都没有直接访问子集合。

我认为延迟加载意味着它只会在被引用时实例化子对象集合？我曾尝试查看类似的问题，但无法弄清楚整个事情，因此希望得到任何澄清。

有趣的是，我一直都设置了这种关系，但只有在我将数据库更改为与子表建立适当的外键关系时才真正注意到异常。

编辑：堆栈跟踪：

堆栈跟踪：

17:39:17] ERROR org.hibernate.LazyInitializationException  - failed to lazily initialize a collection of role: eis.model.PaperOffering.paperOfferingAssessments, no session or session was closed
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: eis.model.PaperOffering.paperOfferingAssessments, no session or session was closed
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:380)
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:372)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:365)
    at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:108)
    at org.hibernate.collection.PersistentSet.toArray(PersistentSet.java:194)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildCollectionNode(JavaScriptBuilder.java:524)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildNode(JavaScriptBuilder.java:365)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildObjectNode(JavaScriptBuilder.java:420)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildNode(JavaScriptBuilder.java:374)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildArrayNode(JavaScriptBuilder.java:507)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildCollectionNode(JavaScriptBuilder.java:524)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildNode(JavaScriptBuilder.java:365)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.build(JavaScriptBuilder.java:191)
    at net.sourceforge.stripes.ajax.JavaScriptResolution.execute(JavaScriptResolution.java:75)
    at net.sourceforge.stripes.controller.DispatcherHelper$7.intercept(DispatcherHelper.java:508)
    at net.sourceforge.stripes.controller.ExecutionContext.proceed(ExecutionContext.java:158)
    at net.sourceforge.stripes.controller.HttpCacheInterceptor.intercept(HttpCacheInterceptor.java:99)
    at net.sourceforge.stripes.controller.ExecutionContext.proceed(ExecutionContext.java:155)
    at net.sourceforge.stripes.controller.BeforeAfterMethodInterceptor.intercept(BeforeAfterMethodInterceptor.java:113)
    at net.sourceforge.stripes.controller.ExecutionContext.proceed(ExecutionContext.java:155)
    at net.sourceforge.stripes.controller.ExecutionContext.wrap(ExecutionContext.java:74)
    at net.sourceforge.stripes.controller.DispatcherHelper.executeResolution(DispatcherHelper.java:502)
    at net.sourceforge.stripes.controller.DispatcherServlet.executeResolution(DispatcherServlet.java:286)
    at net.sourceforge.stripes.controller.DispatcherServlet.service(DispatcherServlet.java:170)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:527)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1216)
    at net.sourceforge.stripes.controller.StripesFilter.doFilter(StripesFilter.java:247)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1187)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:343)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:188)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.session.ConcurrentSessionFilter.doFilter(ConcurrentSessionFilter.java:109)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:149)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1187)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:421)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:493)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:225)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:930)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:358)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:866)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:245)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)
    at org.eclipse.jetty.server.Server.handle(Server.java:351)
    at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:594)
    at org.eclipse.jetty.server.HttpConnection$RequestHandler.content(HttpConnection.java:1059)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:764)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:217)
    at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:424)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:506)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)
    at java.lang.Thread.run(Thread.java:619)
[17:39:17] WARN  net.sourceforge.stripes.ajax.JavaScriptBuilder  - Could not translate property [paperOfferingAssessments] of type [java.util.Set] due to an exception.
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: eis.model.PaperOffering.paperOfferingAssessments, no session or session was closed
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:380)
    at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:372)
    at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:365)
    at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:108)
    at org.hibernate.collection.PersistentSet.toArray(PersistentSet.java:194)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildCollectionNode(JavaScriptBuilder.java:524)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildNode(JavaScriptBuilder.java:365)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildObjectNode(JavaScriptBuilder.java:420)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildNode(JavaScriptBuilder.java:374)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildArrayNode(JavaScriptBuilder.java:507)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildCollectionNode(JavaScriptBuilder.java:524)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.buildNode(JavaScriptBuilder.java:365)
    at net.sourceforge.stripes.ajax.JavaScriptBuilder.build(JavaScriptBuilder.java:191)
    at net.sourceforge.stripes.ajax.JavaScriptResolution.execute(JavaScriptResolution.java:75)
    at net.sourceforge.stripes.controller.DispatcherHelper$7.intercept(DispatcherHelper.java:508)
    at net.sourceforge.stripes.controller.ExecutionContext.proceed(ExecutionContext.java:158)
    at net.sourceforge.stripes.controller.HttpCacheInterceptor.intercept(HttpCacheInterceptor.java:99)
    at net.sourceforge.stripes.controller.ExecutionContext.proceed(ExecutionContext.java:155)
    at net.sourceforge.stripes.controller.BeforeAfterMethodInterceptor.intercept(BeforeAfterMethodInterceptor.java:113)
    at net.sourceforge.stripes.controller.ExecutionContext.proceed(ExecutionContext.java:155)
    at net.sourceforge.stripes.controller.ExecutionContext.wrap(ExecutionContext.java:74)
    at net.sourceforge.stripes.controller.DispatcherHelper.executeResolution(DispatcherHelper.java:502)
    at net.sourceforge.stripes.controller.DispatcherServlet.executeResolution(DispatcherServlet.java:286)
    at net.sourceforge.stripes.controller.DispatcherServlet.service(DispatcherServlet.java:170)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:527)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1216)
    at net.sourceforge.stripes.controller.StripesFilter.doFilter(StripesFilter.java:247)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1187)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:343)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:109)
    at org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:83)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:97)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:100)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:78)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:35)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:188)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:79)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.session.ConcurrentSessionFilter.doFilter(ConcurrentSessionFilter.java:109)
    at org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:355)
    at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:149)
    at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:237)
    at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:167)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1187)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:421)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:119)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:493)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:225)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:930)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:358)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:866)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:117)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:245)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:126)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:113)
    at org.eclipse.jetty.server.Server.handle(Server.java:351)
    at org.eclipse.jetty.server.HttpConnection.handleRequest(HttpConnection.java:594)
    at org.eclipse.jetty.server.HttpConnection$RequestHandler.content(HttpConnection.java:1059)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:764)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:217)
    at org.eclipse.jetty.server.HttpConnection.handle(HttpConnection.java:424)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:506)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:436)
    at java.lang.Thread.run(Thread.java:619)

【问题讨论】：

@mrtrombone 发布堆栈跟踪以及如何检索实体
使用基本命名查询检索实体 - “select p from paperoffering p where year = :year” 在这个特定的例子中，我只使用名称和 id 字段来填充选择列表，所以我可能应该创建一个简单的 DTO 但我只想先了解

标签： java hibernate jpa lazy-loading entitymanager

【解决方案1】：

Lazy 表示当有人调用get(index) 或其他需要对完全初始化集合进行操作的方法时，将加载集合项。 size() 不初始化集合。

您的错误意味着您的代码试图从集合中获取元素，在 Hibernate 会话之外工作。会话之前关闭了一段时间，所以你得到了懒惰的分离集合。

请检查您使用集合操作的代码是否在事务中执行。也许，你需要用@Transactional 注释标记你的方法（如果你使用声明性描述）或者将你的代码放在

TransactionManager tm = //get TransactionManager
try {
    tm.begin();
    //your code
    tm.commit();
} catch (Exception e) {
    tm.rollback();
}

【讨论】：

【解决方案2】：

您确定不访问 toString、hashCode 或 equals-methods 中的集合吗？ hibernate 可以使用后面的 2 来将结果添加到其缓存中。

【讨论】：

不，我没有——当然，子对象（paperofferingassessment）在哈希码和equals中使用了paperoffering，但这会导致问题——关于为什么要实例化它仍然是同样的问题