Revert "HHH-9518 : Exception handling around collection session access needs to be improved"

This reverts commit db475ed716.
This commit is contained in:
Gail Badner 2015-06-16 18:08:19 -07:00
parent b3b43a82bb
commit f1f5c1ae3a
3 changed files with 14 additions and 761 deletions

View File

@ -34,8 +34,6 @@ import java.util.ListIterator;
import javax.naming.NamingException;
import org.jboss.logging.Logger;
import org.hibernate.AssertionFailure;
import org.hibernate.FlushMode;
import org.hibernate.HibernateException;
@ -49,7 +47,6 @@ import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.engine.spi.Status;
import org.hibernate.engine.spi.TypedValue;
import org.hibernate.internal.CoreMessageLogger;
import org.hibernate.internal.SessionFactoryRegistry;
import org.hibernate.internal.util.MarkerObject;
import org.hibernate.internal.util.collections.EmptyIterator;
@ -59,6 +56,7 @@ import org.hibernate.persister.entity.EntityPersister;
import org.hibernate.pretty.MessageHelper;
import org.hibernate.type.ComponentType;
import org.hibernate.type.Type;
import org.jboss.logging.Logger;
/**
* Base class implementing {@link org.hibernate.collection.spi.PersistentCollection}
@ -66,9 +64,7 @@ import org.hibernate.type.Type;
* @author Gavin King
*/
public abstract class AbstractPersistentCollection implements Serializable, PersistentCollection {
private static final CoreMessageLogger LOG = Logger.getMessageLogger(
CoreMessageLogger.class, AbstractPersistentCollection.class.getName()
);
private static final Logger log = Logger.getLogger( AbstractPersistentCollection.class );
private transient SessionImplementor session;
private boolean initialized;
@ -247,7 +243,7 @@ public abstract class AbstractPersistentCollection implements Serializable, Pers
( (Session) session ).close();
}
catch (Exception e) {
LOG.warn( "Unable to close temporary session used to load lazy collection associated to no session" );
log.warn( "Unable to close temporary session used to load lazy collection associated to no session" );
}
session = originalSession;
}
@ -606,9 +602,6 @@ public abstract class AbstractPersistentCollection implements Serializable, Pers
return true;
}
else {
if ( this.session != null ) {
LOG.logCannotUnsetUnexpectedSessionInCollection( generateUnexpectedSessionStateMessage( currentSession ) );
}
return false;
}
}
@ -637,23 +630,26 @@ public abstract class AbstractPersistentCollection implements Serializable, Pers
* @throws HibernateException if the collection was already associated
* with another open session
*/
@Override
public final boolean setCurrentSession(SessionImplementor session) throws HibernateException {
if ( session == this.session ) {
return false;
}
else {
if ( this.session != null ) {
final String msg = generateUnexpectedSessionStateMessage( session );
if ( isConnectedToSession() ) {
if ( isConnectedToSession() ) {
CollectionEntry ce = session.getPersistenceContext().getCollectionEntry( this );
if ( ce == null ) {
throw new HibernateException(
"Illegal attempt to associate a collection with two open sessions. " + msg
"Illegal attempt to associate a collection with two open sessions"
);
}
else {
LOG.logUnexpectedSessionInCollectionNotConnected( msg );
this.session = session;
return true;
throw new HibernateException(
"Illegal attempt to associate a collection with two open sessions: " +
MessageHelper.collectionInfoString(
ce.getLoadedPersister(), this,
ce.getLoadedKey(), session
)
);
}
}
else {
@ -663,50 +659,9 @@ public abstract class AbstractPersistentCollection implements Serializable, Pers
}
}
private String generateUnexpectedSessionStateMessage(SessionImplementor session) {
// NOTE: If this.session != null, this.session may be operating on this collection
// (e.g., by changing this.role, this.key, or even this.session) in a different thread.
// Grab the current role and key (it can still get changed by this.session...)
// If this collection is connected to this.session, then this.role and this.key should
// be consistent with the CollectionEntry in this.session (as long as this.session doesn't
// change it). Don't access the CollectionEntry in this.session because that could result
// in multi-threaded access to this.session.
final String roleCurrent = role;
final Serializable keyCurrent = key;
final StringBuilder sb = new StringBuilder( "Collection : " );
if ( roleCurrent != null ) {
sb.append( MessageHelper.collectionInfoString( roleCurrent, keyCurrent ) );
}
else {
final CollectionEntry ce = session.getPersistenceContext().getCollectionEntry( this );
if ( ce != null ) {
sb.append(
MessageHelper.collectionInfoString(
ce.getLoadedPersister(),
this,
ce.getLoadedKey(),
session
)
);
}
else {
sb.append( "<unknown>" );
}
}
// only include the collection contents if debug logging
if ( LOG.isDebugEnabled() ) {
final String collectionContents = wasInitialized() ? toString() : "<uninitialized>";
sb.append( "\nCollection contents: [" ).append( collectionContents ).append( "]" );
}
return sb.toString();
}
/**
* Do we need to completely recreate this collection when it changes?
*/
@Override
public boolean needsRecreate(CollectionPersister persister) {
// Workaround for situations like HHH-7072. If the collection element is a component that consists entirely
// of nullable properties, we currently have to forcefully recreate the entire collection. See the use

View File

@ -1652,12 +1652,4 @@ public interface CoreMessageLogger extends BasicLogger {
@LogMessage(level = DEBUG)
@Message(value = "Creating pooled optimizer (lo) with [incrementSize=%s; returnClass=%s]", id = 467)
void creatingPooledLoOptimizer(int incrementSize, String name);
@LogMessage(level = WARN)
@Message(value = "An unexpected session is defined for a collection, but the collection is not connected to that session. A persistent collection may only be associated with one session at a time. Overwriting session. %s", id = 470)
void logUnexpectedSessionInCollectionNotConnected(String msg);
@LogMessage(level = WARN)
@Message(value = "Cannot unset session in a collection because an unexpected session is defined. A persistent collection may only be associated with one session at a time. %s", id = 471 )
void logCannotUnsetUnexpectedSessionInCollection(String msg);
}

View File

@ -1,694 +0,0 @@
/*
* Hibernate, Relational Persistence for Idiomatic Java
*
* Copyright (c) 2014, Red Hat Inc. or third-party contributors as
* indicated by the @author tags or express copyright attribution
* statements applied by the authors. All third-party contributions are
* distributed under license by Red Hat Inc.
*
* This copyrighted material is made available to anyone wishing to use, modify,
* copy, or redistribute it subject to the terms and conditions of the GNU
* Lesser General Public License, as published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
* for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this distribution; if not, write to:
* Free Software Foundation, Inc.
* 51 Franklin Street, Fifth Floor
* Boston, MA 02110-1301 USA
*/
package org.hibernate.test.collection.multisession;
import java.util.HashSet;
import java.util.Set;
import javax.persistence.CascadeType;
import javax.persistence.ElementCollection;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.OneToMany;
import javax.persistence.Table;
import org.jboss.logging.Logger;
import org.junit.Test;
import org.hibernate.Hibernate;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.collection.internal.AbstractPersistentCollection;
import org.hibernate.collection.spi.PersistentCollection;
import org.hibernate.engine.spi.CollectionEntry;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.testing.TestForIssue;
import org.hibernate.testing.junit4.BaseCoreFunctionalTestCase;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.fail;
/**
* @author Gail Badner
*/
public class MultipleSessionCollectionTest extends BaseCoreFunctionalTestCase {
private static final Logger log = Logger.getLogger( MultipleSessionCollectionTest.class );
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testSaveOrUpdateOwnerWithCollectionInNewSessionBeforeFlush() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s1 = openSession();
s1.getTransaction().begin();
s1.saveOrUpdate( p );
// try to save the same entity in a new session before flushing the first session
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( p );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testSaveOrUpdateOwnerWithCollectionInNewSessionAfterFlush() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s1 = openSession();
s1.getTransaction().begin();
s1.saveOrUpdate( p );
s1.flush();
// try to save the same entity in a new session after flushing the first session
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( p );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testSaveOrUpdateOwnerWithUninitializedCollectionInNewSession() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s = openSession();
s.getTransaction().begin();
s.persist( p );
s.getTransaction().commit();
s.close();
Session s1 = openSession();
s1.getTransaction().begin();
p = (Parent) s1.get( Parent.class, p.id );
assertFalse( Hibernate.isInitialized( p.children ) );
// try to save the same entity (with an uninitialized collection) in a new session
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( p );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to initialize collection, modify and commit in first session
assertFalse( Hibernate.isInitialized( p.children ) );
Hibernate.initialize( p.children );
p.children.add( new Child() );
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( 2, pGet.children.size());
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testSaveOrUpdateOwnerWithInitializedCollectionInNewSession() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s = openSession();
s.getTransaction().begin();
s.persist( p );
s.getTransaction().commit();
s.close();
Session s1 = openSession();
s1.getTransaction().begin();
p = (Parent) s1.get( Parent.class, p.id );
Hibernate.initialize( p.children );
// try to save the same entity (with an initialized collection) in a new session
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( p );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
//
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testCopyPersistentCollectionReferenceBeforeFlush() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s1 = openSession();
s1.getTransaction().begin();
s1.persist( p );
// Copy p.children into a different Parent before flush and try to save in new session.
Parent pWithSameChildren = new Parent();
pWithSameChildren.children = p.children;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( pWithSameChildren );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testCopyPersistentCollectionReferenceAfterFlush() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s1 = openSession();
s1.getTransaction().begin();
s1.persist( p );
s1.flush();
// Copy p.children into a different Parent after flush and try to save in new session.
Parent pWithSameChildren = new Parent();
pWithSameChildren.children = p.children;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( pWithSameChildren );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testCopyUninitializedCollectionReferenceAfterGet() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s = openSession();
s.getTransaction().begin();
s.persist( p );
s.getTransaction().commit();
s.close();
Session s1 = openSession();
s1.getTransaction().begin();
p = (Parent) s1.get( Parent.class, p.id );
assertFalse( Hibernate.isInitialized( p.children ) );
// Copy p.children (uninitialized) into a different Parent and try to save in new session.
Parent pWithSameChildren = new Parent();
pWithSameChildren.children = p.children;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( pWithSameChildren );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testCopyInitializedCollectionReferenceAfterGet() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s = openSession();
s.getTransaction().begin();
s.persist( p );
s.getTransaction().commit();
s.close();
Session s1 = openSession();
s1.getTransaction().begin();
p = (Parent) s1.get( Parent.class, p.id );
Hibernate.initialize( p.children );
// Copy p.children (initialized) into a different Parent.children and try to save in new session.
Parent pWithSameChildren = new Parent();
pWithSameChildren.children = p.children;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( pWithSameChildren );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testCopyInitializedCollectionReferenceToNewEntityCollectionRoleAfterGet() {
Parent p = new Parent();
Child c = new Child();
p.children.add( c );
Session s = openSession();
s.getTransaction().begin();
s.persist( p );
s.getTransaction().commit();
s.close();
Session s1 = openSession();
s1.getTransaction().begin();
p = (Parent) s1.get( Parent.class, p.id );
Hibernate.initialize( p.children );
// Copy p.children (initialized) into a different Parent.oldChildren (note different collection role)
// and try to save in new session.
Parent pWithSameChildren = new Parent();
pWithSameChildren.oldChildren = p.children;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( pWithSameChildren );
s2.getTransaction().commit();
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit in first session
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
Parent pGet = (Parent) s1.get( Parent.class, p.id );
assertEquals( c.id, pGet.children.iterator().next().id );
session.delete( pGet );
s1.getTransaction().commit();
session.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testDeleteCommitCopyToNewOwnerInNewSession() {
Parent p1 = new Parent();
p1.nickNames.add( "nick" );
Parent p2 = new Parent();
Session s1 = openSession();
s1.getTransaction().begin();
s1.save( p1 );
s1.save( p2 );
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
s1.delete( p1 );
s1.flush();
s1.getTransaction().commit();
// need to commit after flushing; otherwise, will get lock failure when try to move the collection below
assertNull( ( (SessionImplementor) s1 ).getPersistenceContext().getEntry( p1 ) );
CollectionEntry ceChildren = ( (SessionImplementor) s1 ).getPersistenceContext().getCollectionEntry( (PersistentCollection) p1.children );
CollectionEntry ceNickNames = ( (SessionImplementor) s1 ).getPersistenceContext().getCollectionEntry( (PersistentCollection) p1.nickNames );
assertNull( ceChildren );
assertNull( ceNickNames );
assertNull( ( ( AbstractPersistentCollection) p1.children ).getSession() );
assertNull( ( ( AbstractPersistentCollection) p1.oldChildren ).getSession() );
assertNull( ( ( AbstractPersistentCollection) p1.nickNames ).getSession() );
assertNull( ( (AbstractPersistentCollection) p1.oldNickNames ).getSession() );
// Assign the deleted collection to a different entity with same collection role (p2.nickNames)
p2.nickNames = p1.nickNames;
Session s2 = openSession();
s2.getTransaction().begin();
s2.saveOrUpdate( p2 );
s2.getTransaction().commit();
s2.close();
s1.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testDeleteCommitCopyToNewOwnerNewCollectionRoleInNewSession() {
Parent p1 = new Parent();
p1.nickNames.add( "nick" );
Parent p2 = new Parent();
Session s1 = openSession();
s1.getTransaction().begin();
s1.save( p1 );
s1.save( p2 );
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
s1.delete( p1 );
s1.flush();
s1.getTransaction().commit();
// need to commit after flushing; otherwise, will get lock failure when try to move the collection below
assertNull( ( (SessionImplementor) s1 ).getPersistenceContext().getEntry( p1 ) );
CollectionEntry ceChildren = ( (SessionImplementor) s1 ).getPersistenceContext().getCollectionEntry( (PersistentCollection) p1.children );
CollectionEntry ceNickNames = ( (SessionImplementor) s1 ).getPersistenceContext().getCollectionEntry( (PersistentCollection) p1.nickNames );
assertNull( ceChildren );
assertNull( ceNickNames );
assertNull( ( ( AbstractPersistentCollection) p1.children ).getSession() );
assertNull( ( ( AbstractPersistentCollection) p1.oldChildren ).getSession() );
assertNull( ( ( AbstractPersistentCollection) p1.nickNames ).getSession() );
assertNull( ( (AbstractPersistentCollection) p1.oldNickNames ).getSession() );
// Assign the deleted collection to a different entity with different collection role (p2.oldNickNames)
p2.oldNickNames = p1.nickNames;
Session s2 = openSession();
s2.getTransaction().begin();
s2.saveOrUpdate( p2 );
s2.getTransaction().commit();
s2.close();
s1.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testDeleteCopyToNewOwnerInNewSessionBeforeFlush() {
Parent p1 = new Parent();
p1.nickNames.add( "nick" );
Parent p2 = new Parent();
Session s1 = openSession();
s1.getTransaction().begin();
s1.save( p1 );
s1.save( p2 );
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
s1.delete( p1 );
// Assign the deleted collection to a different entity with same collection role (p2.nickNames)
// before committing delete.
p2.nickNames = p1.nickNames;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( p2 );
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit the original delete
s1.getTransaction().commit();
s1.close();
}
@Test
@TestForIssue( jiraKey = "HHH-9518" )
public void testDeleteCopyToNewOwnerNewCollectionRoleInNewSessionBeforeFlush() {
Parent p1 = new Parent();
p1.nickNames.add( "nick" );
Parent p2 = new Parent();
Session s1 = openSession();
s1.getTransaction().begin();
s1.save( p1 );
s1.save( p2 );
s1.getTransaction().commit();
s1.close();
s1 = openSession();
s1.getTransaction().begin();
s1.delete( p1 );
// Assign the deleted collection to a different entity with different collection role (p2.oldNickNames)
// before committing delete.
p2.oldNickNames = p1.nickNames;
Session s2 = openSession();
s2.getTransaction().begin();
try {
s2.saveOrUpdate( p2 );
fail( "should have thrown HibernateException" );
}
catch (HibernateException ex) {
log.error( ex );
s2.getTransaction().rollback();
}
finally {
s2.close();
}
// should still be able to commit the original delete
s1.getTransaction().commit();
s1.close();
}
@Override
public Class<?>[] getAnnotatedClasses() {
return new Class[] {
Parent.class,
Child.class
};
}
@Entity
@Table(name="Parent")
public static class Parent {
@Id
@GeneratedValue
private Long id;
@ElementCollection
private Set<String> nickNames = new HashSet<String>();
@ElementCollection
private Set<String> oldNickNames = new HashSet<String>();
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn
private Set<Child> children = new HashSet<Child>();
@OneToMany(cascade = CascadeType.ALL)
@JoinColumn
private Set<Child> oldChildren = new HashSet<Child>();
}
@Entity
@Table(name="Child")
public static class Child {
@Id
@GeneratedValue
private Long id;
}
}