如何在没有问题的情况下使用JPA 2.0 @ManyToMany [英] How to use JPA 2.0 @ManyToMany without issues

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本文介绍了如何在没有问题的情况下使用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（payment）
 public class PaymentData实现Serializable 
 {
 private Long pk; 
 
私人收藏< PaymentItemData> paymentItem; 
 / ** 
 * minorPaymentItem 
 * 
 * / 
私人收藏< MinorPayItemData> minorPaymentItem; 
 $ b @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; 
 
 $ b $ ** 
 * @param minorPaymentItem minorPaymentItem设置
 * / 
 public void setMinorPaymentItem（final Collection< MinorPayItemData> value）
 {
 this.minorPaymentItem = value; 
 
 $ b @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; 
 
 $ b $ ** 
 *设置属性paymentItem 
 * 
 * @param value -paymentItem 
 * 
 * / 
 public void setPaymentItem（final Collection< PaymentItemData> value）
 {
 this.paymentItem = value; 
} 
 
}

当我运行查询来检索记录来自数据库中的支付表，如 

 查询q = manager.createQuery（从支付数据a中选择一个）; 
 q.getResultList（）;

如果我允许 fetch = FetchType.EAGER @ManyToMany ，我收到以下错误：

  ：org.hibernate.loader.MultipleBagFetchException：无法同时在org.hibernate.loader.BasicLoader.postInstantiate（BasicLoader.java:94）
处获取多个购物袋
 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.hib在org.hibernate.persister.entity.AbstractEntityPersister.postInstantiate（AbstractEntityPersister.java:3191）
 org.hibernate.persister。
在org.hibernate.persister.entity.AbstractEntityPersister.postInstantiate（AbstractEntityPersister.java:3191）
在org.hibernate.persister。 entity.SingleTableEntityPersister.postInstantiate（SingleTableEntityPersister.java:728）LT 
。在org.hibernate.impl.SessionFactoryImpl&;初始化>（SessionFactoryImpl.java:348）
。在org.hibernate.cfg.Configuration.buildSessionFactory （Configuration.java:1845）
 at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory（Ejb3Configuration.java:906）
 ... 39 more

但是，如果我删除 fetch = FetchType.EAGER 并将其保留为 @ManyToMany ，我将会有例外情况

  org.hibernate.LazyInitializationException：未能延迟初始化角色：com.data.PaymentData.paymentItem，没有会话或会话在org.h关闭
 ¶收藏文章登录我的社区来说两句吧...表情删除后不可恢复，是否删除取消确定图片正在上传，请稍后...正在操作中...正在操作中... ...正在操作中...正在操作中... ...正在操作中...正在操作中... AbstractPersistentCollection.java:368）
 at org.hibernate.collection.AbstractPersistentCollection.read（AbstractPersistentCollection.java:111）
 at org.hibernate.collection.PersistentBag.toString（PersistentBag.java:506）
在java.lang.String.valueOf（String.java:2826）$ b $在java.lang.StringBuilder.append（StringBuilder.java:115）
在com.niu.util.Util.toString （Util.java:131）
 at com.niu.util.data.BaseData.toString（BaseData.java:107）
 at java.lang.String.valueOf（String.java:2826）$ b java.lang.StringBuilder.append（StringBuilder.java:115）
 java.util.AbstractCollection.toString（Ab （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）
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）
 at com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept（Method （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）
在com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept（ParametersInterceptor.java:207）
在com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept（MethodFilterIntercepto r.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）
在com.open symphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept（ScopedModelDrivenInterceptor.java:141）
处org.apache.struts2.interceptor com.opensymphony.xwork2.DefaultActionInvocation.invoke（DefaultActionInvocation.java:248）
。 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）
 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.xwork 2.interceptor.MethodFilterInterceptor.intercept（MethodFilterInterceptor.java:98）
 at com.opensymphony.xwork2.DefaultActionInvocation.invoke（DefaultActionInvocation.java:248）
 at com.opensymphony.xwork2.interceptor.I18nInterceptor。截取（I18nInterceptor.java:176）
 at com.opensymphony.xwork2.DefaultActionInvocation.invoke（DefaultActionInvocation.java:248）
 at org.apache.struts2.interceptor.ServletConfigInterceptor.intercept（ServletConfigInterceptor.java： ）
 at com.opensymphony.xwork2.DefaultActionInvocation.invoke（DefaultActionInvocation.java:248）
 at com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept（AliasInterceptor.java:190）
在com.opensymphony.xwork2.DefaultActionInvocation.invoke（DefaultActionInvocation.java:248）
 at com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept（ExceptionMappingInterceptor.java:187）
 at com.opensymphony.xwork2 .DefaultActionInvocation.invoke（DefaultAc tionInvocation.java:248）
 at org.apache.struts2.impl.StrutsActionProxy.execute（StrutsActionProxy.java:52）
 at org.apache.struts2.dispatcher.Dispatcher.serviceAction（Dispatcher.java： 
 at org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction（ExecuteOperations.java:77）
 at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter（StrutsPrepareAndExecuteFilter。 
 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）
在org.apache.catalina.valves.ErrorReportValve.invoke（ErrorReportValve.java:100）
在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）
。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）$ b $在java.util.concurrent.ThreadPoolExecutor $ Worker.runTask（ThreadPoolExecutor.java:886）
在java.util.concurrent.ThreadPoolExecutor $ Worker.run（ThreadPoolExecutor.java:908）$ b $在java.lang.Thread.run（Thread.java:662）
  
 
我做错了什么
解决方案 
为避免 MultipleBagFetchException ，而不是使用 FetchType.EAGER ，请尝试使用 @LazyCollection（LazyCollectionOption.FALSE）如下例所示：
  @ 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））
 public Collection< MinorPayItemData> getMinorPaymentItem（）
 {
 return minorPaymentItem; 
} 
  
以下是 docs ： 
 
 
     
     
  •  
     
     <@> @LazyCollection：定义@ManyToMany和
     @OneToMany关联的懒惰选项。 LazyCollectionOption可以是TRUE（
    集合是懒惰的，当它的状态被访问时会被加载），
     EXTRA（集合是懒惰的，所有的操作都会尝试避免
    集合的加载，这个对于大型集合
    特别有用，当加载所有元素时是不必要的）和FALSE（关联
    不懒惰）
     
     
    •  
     
  •  
     
      @Fetch：定义了用于加载关联的抓取策略。 
     FetchMode可以是SELECT（当需要加载关联
    时触发选择），SUBSELECT（仅适用于集合，使用
    子选择策略 - 请参考Hibernate Reference 
    文档以获取更多信息）或JOIN（使用SQL JOIN在加载所有者实体时加载
    关联）。 JOIN覆盖任何
     lazy属性（通过JOIN策略加载的关联不能
    懒惰）。
     
     
     
    •  
     
 
 
 
我希望它有帮助
 
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


                        
这篇关于如何在没有问题的情况下使用JPA 2.0 @ManyToMany的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

                        
                    

                    

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