如何毫无问题地使用 JPA 2.0 @ManyToMany [英] How to use JPA 2.0 @ManyToMany without issues
本文介绍了如何毫无问题地使用 JPA 2.0 @ManyToMany的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我在开发中使用 JPA 2.0 和 Spring.我的实体类包含两个 @ManyToMany 关系.
@Entity("支付")公共类 PaymentData 实现 Serializable{私长pk；私人收藏<PaymentItemData>付款项；/*** 次要付款项**/私人收藏<MinorPayItemData>次要付款项；@ManyToMany(fetch=FetchType.EAGER)@JoinTable(name = "payitem_m_assig",加入列 =@JoinColumn(name = "pay_item_id", nullable = false),inverseJoinColumns =@JoinColumn(name = "minor_pay_item_id", nullable = false))公共集合<MinorPayItemData>getMinorPaymentItem(){返回minorPaymentItem；}/*** @param minorPaymentItem 要设置的 minorPaymentItem*/公共无效 setMinorPaymentItem(最终集合 值){this.minorPaymentItem = 价值；}@ManyToMany(fetch=FetchType.EAGER)@JoinTable(name = "payitem_assigned",加入列 =@JoinColumn(name = "pay_item_id", nullable = false),inverseJoinColumns =@JoinColumn(name = "pay_item_id", nullable = false))公共集合<PaymentItemData>获取付款项(){返回付款项；}/*** 设置属性paymentItem** @param 值 -paymentItem**/public void setPaymentItem(final Collection value){this.paymentItem = 价值；}} 当我运行查询以从数据库中的支付表中检索记录时，例如
Query q = manager.createQuery("select a from PaymentData a");q.getResultList();如果我允许 @ManyToMany 上的 fetch=FetchType.EAGER，我会收到以下错误
引起:org.hibernate.loader.MultipleBagFetchException:不能同时获取多个包在 org.hibernate.loader.BasicLoader.postInstantiate(BasicLoader.java:94)在 org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:119)在 org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:71)在 org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:54)在 org.hibernate.loader.entity.BatchingEntityLoader.createBatchingEntityLoader(BatchingEntityLoader.java:133)在 org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1914)在 org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1937)在 org.hibernate.persister.entity.AbstractEntityPersister.createLoaders(AbstractEntityPersister.java:3205)在 org.hibernate.persister.entity.AbstractEntityPersister.postInstantiate(AbstractEntityPersister.java:3191)在 org.hibernate.persister.entity.SingleTableEntityPersister.postInstantiate(SingleTableEntityPersister.java:728)在 org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:348)在 org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1845)在 org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:906)... 39 更多但如果我删除 fetch=FetchType.EAGER 并将其保留为 @ManyToMany，我将遇到异常
org.hibernate.LazyInitializationException: 延迟初始化角色集合失败:com.data.PaymentData.paymentItem，没有会话或会话被关闭在 org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:383)在 org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:375)在 org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:368)在 org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:111)在 org.hibernate.collection.PersistentBag.toString(PersistentBag.java:506)在 java.lang.String.valueOf(String.java:2826)在 java.lang.StringBuilder.append(StringBuilder.java:115)在 com.niu.util.Util.toString(Util.java:131)在 com.niu.util.data.BaseData.toString(BaseData.java:107)在 java.lang.String.valueOf(String.java:2826)在 java.lang.StringBuilder.append(StringBuilder.java:115)在 java.util.AbstractCollection.toString(AbstractCollection.java:422)在 java.lang.String.valueOf(String.java:2826)在 java.io.PrintStream.println(PrintStream.java:771)在 org.apache.tomcat.util.log.SystemLogHandler.println(SystemLogHandler.java:269)在 sun.reflect.GeneratedMethodAccessor1861.invoke(未知来源)在 sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)在 java.lang.reflect.Method.invoke(Method.java:597)在 com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452)在 com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254)在 com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)在 com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)在 com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)在 com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.niu.web.common.interceptor.ApplicationModelDrivenInterceptor.intercept(ApplicationModelDrivenInterceptor.java:31)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 org.apache.struts2.interceptor.ProfilingActivationInterceptor.intercept(ProfilingActivationInterceptor.java:104)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:270)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)在 com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)在 com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)在 org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)在 org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:498)在 org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)在 org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)在 org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)在 org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)在 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)在 org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)在 org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)在 org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)在 org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)在 org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)在 org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)在 org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)在 org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)在 org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)在 org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)在 java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)在 java.lang.Thread.run(Thread.java:662)我做错了什么
解决方案
为了避免MultipleBagFetchException，不要使用FetchType.EAGER，尝试使用@LazyCollection(LazyCollectionOption.FALSE) 如本例所示:
@ManyToMany@LazyCollection(LazyCollectionOption.FALSE)@JoinTable(name = "payitem_m_assig", joinColumns = @JoinColumn(name = "pay_item_id", nullable = e), inverseJoinColumns = @JoinColumn(name = "minor_pay_item_id", nullable = false))公共集合<MinorPayItemData>getMinorPaymentItem(){返回minorPaymentItem；}这是来自 docs 的简短描述:
- <块引用>
@LazyCollection:定义@ManyToMany 和@OneToMany 关联.LazyCollectionOption 可以是 TRUE(集合是惰性的，将在访问其状态时加载)，EXTRA(集合是惰性的，所有操作都会尽量避免集合加载，这对于大型集合特别有用当不需要加载所有元素时)和 FALSE(关联不懒)
- <块引用>
@Fetch:定义用于加载关联的获取策略.FetchMode可以是SELECT(关联时触发一个select需要加载)，SUBSELECT(仅适用于集合，使用子选择策略 - 请参考 Hibernate Reference有关更多信息的文档)或 JOIN(使用 SQL JOIN 加载加载所有者实体时的关联).JOIN 覆盖任何惰性属性(通过 JOIN 策略加载的关联不能懒惰).
希望对你有帮助
I am using JPA 2.0 and Spring in my development. My entity class contains two @ManyToMany relationships.
@Entity("payment")
public class PaymentData implements Serializable
{
private Long pk;
private Collection<PaymentItemData> paymentItem;
/**
* minorPaymentItem
*
*/
private Collection<MinorPayItemData> minorPaymentItem;
@ManyToMany(fetch=FetchType.EAGER)
@JoinTable(name = "payitem_m_assig",
joinColumns =
@JoinColumn(name = "pay_item_id", nullable = false),
inverseJoinColumns =
@JoinColumn(name = "minor_pay_item_id", nullable = false))
public Collection<MinorPayItemData> getMinorPaymentItem()
{
return minorPaymentItem;
}
/**
* @param minorPaymentItem the minorPaymentItem to set
*/
public void setMinorPaymentItem(final Collection<MinorPayItemData> value)
{
this.minorPaymentItem = value;
}
@ManyToMany(fetch=FetchType.EAGER)
@JoinTable(name = "payitem_assigned",
joinColumns =
@JoinColumn(name = "pay_item_id", nullable = false),
inverseJoinColumns =
@JoinColumn(name = "pay_item_id", nullable = false))
public Collection<PaymentItemData> getPaymentItem()
{
return paymentItem;
}
/**
* Set the property paymentItem
*
* @param value -paymentItem
*
*/
public void setPaymentItem(final Collection<PaymentItemData> value)
{
this.paymentItem = value;
}
}
When i run a query to retrieve records from the payment table in the database, like
Query q = manager.createQuery("select a from PaymentData a");
q.getResultList();
If i allow the fetch=FetchType.EAGER on the @ManyToMany, I get the following errors
Caused by: org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags
at org.hibernate.loader.BasicLoader.postInstantiate(BasicLoader.java:94)
at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:119)
at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:71)
at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:54)
at org.hibernate.loader.entity.BatchingEntityLoader.createBatchingEntityLoader(BatchingEntityLoader.java:133)
at org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1914)
at org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1937)
at org.hibernate.persister.entity.AbstractEntityPersister.createLoaders(AbstractEntityPersister.java:3205)
at org.hibernate.persister.entity.AbstractEntityPersister.postInstantiate(AbstractEntityPersister.java:3191)
at org.hibernate.persister.entity.SingleTableEntityPersister.postInstantiate(SingleTableEntityPersister.java:728)
at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:348)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1845)
at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:906)
... 39 more
But if i remove fetch=FetchType.EAGER and leave it as @ManyToMany, i will have the exception
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: com.data.PaymentData.paymentItem, no session or session was closed
at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:383)
at org.hibernate.collection.AbstractPersistentCollection.throwLazyInitializationExceptionIfNotConnected(AbstractPersistentCollection.java:375)
at org.hibernate.collection.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:368)
at org.hibernate.collection.AbstractPersistentCollection.read(AbstractPersistentCollection.java:111)
at org.hibernate.collection.PersistentBag.toString(PersistentBag.java:506)
at java.lang.String.valueOf(String.java:2826)
at java.lang.StringBuilder.append(StringBuilder.java:115)
at com.niu.util.Util.toString(Util.java:131)
at com.niu.util.data.BaseData.toString(BaseData.java:107)
at java.lang.String.valueOf(String.java:2826)
at java.lang.StringBuilder.append(StringBuilder.java:115)
at java.util.AbstractCollection.toString(AbstractCollection.java:422)
at java.lang.String.valueOf(String.java:2826)
at java.io.PrintStream.println(PrintStream.java:771)
at org.apache.tomcat.util.log.SystemLogHandler.println(SystemLogHandler.java:269)
at sun.reflect.GeneratedMethodAccessor1861.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:452)
at com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:291)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:254)
at com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:176)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:133)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:207)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:190)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:75)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:94)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.niu.web.common.interceptor.ApplicationModelDrivenInterceptor.intercept(ApplicationModelDrivenInterceptor.java:31)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.interceptor.ProfilingActivationInterceptor.intercept(ProfilingActivationInterceptor.java:104)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:270)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:176)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:190)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:187)
at com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:248)
at org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:52)
at org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:498)
at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:77)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:91)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:462)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
What am i doing wrong
解决方案
To avoid the MultipleBagFetchException, instead of using FetchType.EAGER, try using the @LazyCollection(LazyCollectionOption.FALSE) as in this example:
@ManyToMany
@LazyCollection(LazyCollectionOption.FALSE)
@JoinTable(name = "payitem_m_assig", joinColumns = @JoinColumn(name = "pay_item_id", nullable = e), inverseJoinColumns = @JoinColumn(name = "minor_pay_item_id", nullable = false))
public Collection<MinorPayItemData> getMinorPaymentItem()
{
return minorPaymentItem;
}
Here is a small description of from the docs:
@LazyCollection: defines the lazyness option on @ManyToMany and @OneToMany associations. LazyCollectionOption can be TRUE (the collection is lazy and will be loaded when its state is accessed), EXTRA (the collection is lazy and all operations will try to avoid the collection loading, this is especially useful for huge collections when loading all the elements is not necessary) and FALSE (association not lazy)
@Fetch: defines the fetching strategy used to load the association. FetchMode can be SELECT (a select is triggered when the association needs to be loaded), SUBSELECT (only available for collections, use a subselect strategy - please refers to the Hibernate Reference Documentation for more information) or JOIN (use a SQL JOIN to load the association while loading the owner entity). JOIN overrides any lazy attribute (an association loaded through a JOIN strategy cannot be lazy).
I hope it helps
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