How to Fetch @OneToMany and @ManyToMany Entities

问题

my issue is very related to the following:
Why am I getting a Hibernate LazyInitializationException in this Spring MVC web application when the data displays correctly?

I have the following properties on a particular entity:

@OneToMany(fetch = FetchType.EAGER, cascade = {CascadeType.REMOVE})
@JoinColumn(referencedColumnName = "id", name = "ID_FORMAT_FILE")
private List<ColumnFormat> columnList;
@ManyToMany(fetch = FetchType.EAGER)
@JoinTable(name = "FILEFORMAT_ORIGINATOR", joinColumns = @JoinColumn(name =   "FILEFORMAT_ID", referencedColumnName = "id")
    , inverseJoinColumns = @JoinColumn(name = "ORIGINATOR_ID", referencedColumnName = "id"))
private List<Originator> originators;

As you might have noticed I have an Eager Fetch type on both relations, but it is giving the following:

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:902)
    ... 33 more

I must access both lists List<ColumnFormat> columnList and List<Originator> originators on different beans, but if both are of Fetch Type Eager I get the above problem, and if one of them is Lazy I get the following:

Caused by: org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: xxx.xxx.xxx.xxx.FileFormat.originators, 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.readElementExistence(AbstractPersistentCollection.java:157)
    at org.hibernate.collection.PersistentBag.contains(PersistentBag.java:262)
    at java.util.ArrayList.batchRemove(ArrayList.java:632)
    at java.util.ArrayList.removeAll(ArrayList.java:605)
    at xxx.xxx.xxx.xxx.bean.FileFormatEdit.init(FileFormatEdit.java:1040)
    ... 75 more

Is there a way to retrieve the lists on the different beans without having these problems?

回答1:

Haven't encountered this problem before, but just googling "cannot simultaneously fetch multiple bags" returns this link on the Hibernate forums.

One of the blog posts in that link may contain the solution you're looking for.

回答2:

I deleted all fetch=FetchType.EAGER and it work correct. I´m usign Hibernate 3.5.6-Final, Spring 3.0.4 and Junit 4. I think fetch-EAGER is by default, because my object loads all children.

This is sessionFactory:

<bean id="sessionFactory" class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"
    p:dataSource-ref="dataSource"
    p:packagesToScan="org.pfc.modelo">

    <property name="hibernateProperties">
        <props>
            <prop key="dialect">org.hibernate.dialect.Oracle10gDialect</prop>
            <prop key="show_sql">true</prop>
            <prop key="format_sql">true</prop>
        </props>
    </property>
</bean>

This is class:

@Entity
@Table(name="D_ACTIVIDAD")
public class Actividad implements Serializable {


private static final long serialVersionUID = 1L;

@Id
@SequenceGenerator(sequenceName="SQ_ACTIVIDAD",name="seqActividad")
@GeneratedValue(strategy=GenerationType.SEQUENCE,generator="seqActividad")
private Integer idActividad;

@Column(name="FECHA",nullable=false)
@Temporal(TemporalType.TIMESTAMP)
private Calendar fecha;

@Column(name="TITULO",nullable=false)
private String titulo;

@Column(name="TEXTO",nullable=false)
private String texto;

@ManyToOne
@JoinColumn(name="IDASOCIACION")
private Asociacion asociacion;

@OneToMany(mappedBy="actividad",cascade=CascadeType.ALL,orphanRemoval=true)
private List<ComentarioActividad> comentarios;

@OneToMany(mappedBy="actividad",cascade=CascadeType.ALL,orphanRemoval=true)
@OrderBy(value="fecha")
private List<Documento> documentos;

     //set and get methods 
     ...........
     ...........
     ...........

   }

来源：https://stackoverflow.com/questions/5507077/how-to-fetch-onetomany-and-manytomany-entities

标签

java

hibernate

fetch