Hibernate3: Cannot simultaneously fetch multiple bags

[ericmacau]

Hello,

I don't know why it will raise the "Cannot simultaneously fetch multiple bags" exception, please help and teach me how can I solve the problem?

@Entity
@Table(name="EventNotes")
public class Notes implements Serializable {
 public static final long serialVersionUID = 1L;

 protected long id;
 protected User creator;


 /**
 * @return the creator
 */
 @ManyToOne( cascade = {CascadeType.PERSIST, CascadeType.MERGE} )
 @JoinTable(name="USER_NOTES",
 joinColumns = @JoinColumn(name="NOTES_ID"),
 inverseJoinColumns = @JoinColumn(name="USER_ID")
 )
 public User getCreator() {

 return this.creator;
 }

 /**
 * @param creator the creator to set
 */
 public void setCreator(User creator) {

 this.creator = creator;
 }



 /**
 * @return the id
 */
 @Id
 @GeneratedValue(strategy = GenerationType.AUTO)
 public long getId() {

 return this.id;
 }

 /**
 * @param id the id to set
 */
 public void setId(long id) {

 this.id = id;
 }


}

@Entity
@Table(name="USERS")
public class User implements Serializable {
 public static final long serialVersionUID = 1L;

 private String username;

 private String password;


 private String firstName;
 private String lastName;
 private String displayName;
 private String gender;


 private boolean activate;

 private Collection<Role> roles = new ArrayList<Role>();
 private Collection<Group> groups = new ArrayList<Group>();




 @Transient
 public boolean isActivate() {
 return activate;
 }


 public boolean getActivate() {
 return activate;
 }

 public void setActivate(boolean activate) {
 this.activate = activate;
 }

 public String getPassword() {
 return password;
 }

 public void setPassword(String password) {
 this.password = password;
 }

 @Id
 //@GeneratedValue(strategy = GenerationType.AUTO)
 public String getUsername() {
 return username;
 }

 public void setUsername(String username) {
 this.username = username;
 }



 public String getFirstName() {
 return firstName;
 }

 public void setFirstName(String firstName) {
 this.firstName = firstName;
 }

 public String getLastName() {
 return lastName;
 }

 public void setLastName(String lastName) {
 this.lastName = lastName;
 }




 public String getDisplayName() {
 return displayName;
 }

 public void setDisplayName(String displayName) {
 this.displayName = displayName;
 }





 public String getGender() {
 return gender;
 }

 public void setGender(String gender) {
 this.gender = gender;
 }

 @ManyToMany(cascade = {CascadeType.REMOVE},
 fetch = FetchType.EAGER,
 targetEntity=Role.class)
 @JoinTable(
 name="USER_ROLE_LINK",
 joinColumns={@JoinColumn(name="username")},
 inverseJoinColumns={@JoinColumn(name="rolename")}
 )
 public Collection<Role> getRoles() {
 return roles;
 }


 public void setRoles(Collection<Role> roles) {
 this.roles = roles;
 }

 @Transient
 public void addRole(Role role) {
 this.roles.add(role);
 }


 @ManyToMany(cascade = {CascadeType.REMOVE},
 fetch = FetchType.LAZY,
 targetEntity=Group.class)
 @JoinTable(
 name="USER_GROUP_LINK",
 joinColumns={@JoinColumn(name="username")},
 inverseJoinColumns={@JoinColumn(name="groupname")}
 )
 public Collection<Group> getGroups() {
 return groups;
 }



 public void setGroups(Collection<Group> groups) {
 this.groups = groups;
 }

 @Transient
 public void addGroup(Group group) {
 groups.add(group);
 }



 @Transient
 public String toString() {
 StringBuffer buf = new StringBuffer();

 buf.append("=== " + username + "===\n");
 buf.append(displayName + "\n");

 Iterator rs = roles.iterator();
 while(rs.hasNext()) {
 Role r = (Role)rs.next();
 buf.append(r);
 }

 Iterator gs = groups.iterator();
 while(rs.hasNext()) {
 Group g = (Group)rs.next();
 buf.append(g);
 }


 return buf.toString();
 }

}

javax.persistence.PersistenceException: org.hibernate.HibernateException: cannot simultaneously fetch multiple bags
 at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:737)
 at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:121)
 at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:51)
 at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:33)
 at mo.reales.util.HibernateUtil.initFactory(HibernateUtil.java:40)
 at mo.reales.util.HibernateUtil.initFactory(HibernateUtil.java:35)
 at mo.reales.web.ServiceStartupListener.contextInitialized(ServiceStartupListener.java:69)
 at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3763)
 at org.apache.catalina.core.StandardContext.start(StandardContext.java:4211)
 at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:759)
 at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:739)
 at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:524)
 at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:904)
 at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:867)
 at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:474)
 at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1122)
 at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:310)
 at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent(LifecycleSupport.java:119)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1021)
 at org.apache.catalina.core.StandardHost.start(StandardHost.java:718)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1013)
 at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:442)
 at org.apache.catalina.core.StandardService.start(StandardService.java:450)
 at org.apache.catalina.core.StandardServer.start(StandardServer.java:709)
 at org.apache.catalina.startup.Catalina.start(Catalina.java:551)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
 at java.lang.reflect.Method.invoke(Method.java:585)
 at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:294)
 at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:432)
Caused by: org.hibernate.HibernateException: cannot simultaneously fetch multiple bags
 at org.hibernate.loader.BasicLoader.postInstantiate(BasicLoader.java:66)
 at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:75)
 at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:43)
 at org.hibernate.loader.entity.EntityLoader.<init>(EntityLoader.java:33)
 at org.hibernate.loader.entity.BatchingEntityLoader.createBatchingEntityLoader(BatchingEntityLoader.java:103)
 at org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1748)
 at org.hibernate.persister.entity.AbstractEntityPersister.createEntityLoader(AbstractEntityPersister.java:1752)
 at org.hibernate.persister.entity.AbstractEntityPersister.createLoaders(AbstractEntityPersister.java:2982)
 at org.hibernate.persister.entity.AbstractEntityPersister.postInstantiate(AbstractEntityPersister.java:2975)
 at org.hibernate.persister.entity.SingleTableEntityPersister.postInstantiate(SingleTableEntityPersister.java:690)
 at org.hibernate.impl.SessionFactoryImpl.<init>(SessionFactoryImpl.java:290)
 at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1294)
 at org.hibernate.cfg.AnnotationConfiguration.buildSessionFactory(AnnotationConfiguration.java:915)
 at org.hibernate.ejb.Ejb3Configuration.buildEntityManagerFactory(Ejb3Configuration.java:730)
 ... 30 more

[andydale]

Hi,

The "problem" comes from the following code:

private Collection<Role> roles = new ArrayList<Role>();
private Collection<Group> groups = new ArrayList<Group>();

A Collection is treated as a "bag". You have have some possibilities to fix it.

An easy solution is to use the @CollectionID. Another solution would be to change them to List<> and then use the @IndexColum, and the final solution is to change the to Set<>. You must read up on Hibernate Collection mapping first, to see whats suits your data model best.

Go to this URL:

http://www.hibernate.org/hib_docs/annotations/reference/en/html/entity.html#entity-mapping-association

Cheers,

Andy