How to use JPA 2.0 @ManyToMany without issues
hibernate, jpa, jpa-2.0, struts2
Solution
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
Problem
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