Description J F 2011-10-20 08:11:27 EDT

Created attachment 205614 [details]
Examples

Eclipse Persistence Services - 2.4.0.v20110824-r9956
JDK build 1.6.0_27-b07 
Windows Server 2008 SP2 win32

The following program contains 3 simple Entities, A singleton from which I get Container entities which are filled with Item Entities.
The Container owns an ordered list of items.
In a postload handler for Container I check that the list of items never contains null as I do not intend it ever to contain null. I do not remove items from the list or create null items in this example.
The postload handler contains an error message and exit when a problem is detected.
The problem seems to occur when the container entities changes are being merged back into the cache after their item lists have been added to during the second transaction. 
At the beginning of the merge the instance of container which I have just changed is fine, and the cached 'original' is fine.
However when org.eclipse.persistence.internal.queries.OrderedListContainerPolicy#public void mergeChanges(CollectionChangeRecord changeRecord, Object valueOfTarget, boolean shouldMergeCascadeParts, MergeManager mergeManager, AbstractSession targetSession) is called 
it fails to find the added Item eventhough it goes down the //getChangeType == add leg of the code. It seems that an IdentityHashMap is not returning the correct object. The result is that null is added into the cached 'target ' of the merge.
Note:
Every run of this program does NOT give rise to the error. However increasing the number of Containers to 100 almost always results in the problem on my win32 java VM ( max mem is 1024mb )

The program is run with static weaving agent 
-javaagent:C:\development\eclipselink\eclipselink-plugins-2.4.0.v20110824-r9956\org.eclipse.persistence.core_2.4.0.v20110824-r9956.jar.
If I run it without this, i.e. using dynamic weaving, then it does not have the problem even with large numbers of containers.

Here is the console output I see when running this;

The Customizer has been started
Customize a ServerSession(
DatabaseAccessor(disconnected)
H2Platform)
Customize session called TestSimpleOrderedLists_memPU
Found PersonHealth
[EL Info]: 2011-10-13 11:27:28.675--ServerSession(23108627)--EclipseLink, version: Eclipse Persistence Services - 2.4.0.v20110824-r9956
[EL Info]: 2011-10-13 11:27:28.849--ServerSession(23108627)--TestSimpleOrderedLists_memPU login successful
PreInsertEvent: 0$008b1689-73f1-421c-8323-82a212c65c39
AboutToInsertEvent: 0$008b1689-73f1-421c-8323-82a212c65c39
PreUpdateWithChangesEvent: 0$008b1689-73f1-421c-8323-82a212c65c39
PreUpdateWithChangesEvent: 0$008b1689-73f1-421c-8323-82a212c65c39
PreInsertEvent: 0$ff58e277-1583-46b1-b01f-e0dd65247dbc
PreUpdateWithChangesEvent: 0$008b1689-73f1-421c-8323-82a212c65c39
AboutToUpdateEvent: 0$008b1689-73f1-421c-8323-82a212c65c39
AboutToInsertEvent: 0$ff58e277-1583-46b1-b01f-e0dd65247dbc
PreUpdateWithChangesEvent: 0$ff58e277-1583-46b1-b01f-e0dd65247dbc
PreUpdateWithChangesEvent: 0$ff58e277-1583-46b1-b01f-e0dd65247dbc
1: Commit it!
PreUpdateWithChangesEvent: 0$ff58e277-1583-46b1-b01f-e0dd65247dbc
AboutToUpdateEvent: 0$ff58e277-1583-46b1-b01f-e0dd65247dbc
PostMergeEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
PostMergeEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
1: Committed!
PostCloneEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
PostCloneEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
PreUpdateWithChangesEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
PreUpdateWithChangesEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
PreUpdateWithChangesEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
PreUpdateWithChangesEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
PreUpdateWithChangesEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
PreUpdateWithChangesEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
2: Commit it!
PostMergeEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
PostMergeEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
!!!!!!!!! PostMergeEvent: 1$008b1689-73f1-421c-8323-82a212c65c39 source contains null
2: Committed!
PostCloneEvent: 2$ff58e277-1583-46b1-b01f-e0dd65247dbc
PostCloneEvent: 1$008b1689-73f1-421c-8323-82a212c65c39
!!!!!!!!! PostCloneEvent: 1$008b1689-73f1-421c-8323-82a212c65c39 original contains null
!!!!!!!!! PostCloneEvent: 1$008b1689-73f1-421c-8323-82a212c65c39 source contains null
FOUND IT!!!!


Code: [Select all] [Show/ hide]
package uk.co.his.test.simpleol;

import java.io.IOException;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

public class Main {

	private static final int NumItemsPerContainer = 2; //10;
	private static final int NumContainers = 2; //100;
	//private static final int NumContainersForStage2 = 20;
	
	
	
	
	
	public static void runContain2Test() {
		EntityManagerFactory emf = Persistence.createEntityManagerFactory("TestSimpleOrderedLists_memPU");
		EntityManager em = emf.createEntityManager();
		em.getTransaction().begin();

		
		Singleton singleton = Singleton.getInstance(em);
		
		singleton = Singleton.getInstance(em);
		for(int i = 1; i <= NumContainers; i++) {
			Container cont = singleton.containerAddNew(new Container(), em);
			for(int j = 1; j <= NumItemsPerContainer; j++) {
				cont.itemsAddNew(new Item(j), em);
			}
			cont.setDummyProp(i);
		}
		
		System.err.flush();
		System.out.flush();
		System.out.println("1: Commit it!");
		em.getTransaction().commit();
		em.close();
		System.out.println("1: Committed!");
		System.err.flush();
		System.out.flush();
		
		em = emf.createEntityManager();
		em.getTransaction().begin();
		

		singleton = Singleton.getInstance(em);
		for(Container container: singleton.getContainers()) {
			int beginIndex = NumItemsPerContainer;
			container.itemsAddNew(new Item(++beginIndex), em);
			container.itemsAddNew(new Item(++beginIndex), em);
			container.itemsAddNew(new Item(++beginIndex), em);
			//container.setDummyProp(container.getDummyProp() * 10);
		}
		em.flush();

		
/*		for(int i = 1; i <= NumContainersForStage2; i++) {
			Container cont = singleton.containerAddNew(new Container(), em);
			for(int j = 1; j < NumItemsPerContainer; j++) {
				cont.itemsAddNew(new Item(j), em);
			}
			cont.setDummyProp(NumContainers + i);
		}
		for(Container container: singleton.getContainers()) {
			for(Item item: container.getItems()) {
				item.setDummyProp(item.getDummyProp() * 10);
			}
		}*/
		
		System.out.println("2: Commit it!");
		em.getTransaction().commit();
		em.close();
		System.err.flush();
		System.out.flush();
		System.out.println("2: Committed!");

		
		em = emf.createEntityManager();
		em.getTransaction().begin();
		
		singleton = Singleton.getInstance(em);
		for(Container container: singleton.getContainers()) {
			for(@SuppressWarnings("unused") Item item: container.getItems()) {
				System.out.print(".");
			}
		}

		System.err.flush();
		System.out.flush();
		System.out.println("3: Commit it!");
		em.getTransaction().commit();
		em.close();
		System.err.flush();
		System.out.flush();
		System.out.println("3: Committed!");
		
		
		System.err.flush();
		System.out.flush();
		System.out.println("Dones!");
	}
	
	
	/**
	 * @param args
	 * @throws IOException 
	 */
	public static void main(String[] args) throws IOException {

		runContain2Test();

	}

}

package uk.co.his.test.simpleol;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

import javax.persistence.CascadeType;
import javax.persistence.Entity;
import javax.persistence.EntityManager;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.OneToMany;
import javax.persistence.Version;

@Entity
@NamedQueries({
})
public class Singleton {

	@Version private int version;
	
	@Id
	protected String id = "1";

	public static Singleton getInstance(EntityManager em) {
		Singleton c = em.find(Singleton.class, "1");
		if (c == null) {
			c = new Singleton();
			em.persist(c);
		}
		return c;
	}
	
	@OneToMany(cascade=CascadeType.ALL, mappedBy="singleton")
    private java.util.Set<Container>  containers  = new java.util.HashSet<Container>();
	
	protected  Container containerAddNew(Container newObj, EntityManager em) {
	    newObj.setUUID();
	    newObj.setTimestamp(createTimestamp());
	    em.persist(newObj);
	    containers.add(newObj);
	    newObj.setSingleton(this);
	    newObj.itemsAddNew(new Item(0), em);
	    return newObj;
	}
	
	public java.util.Set<Container> getContainers() {
		return containers;
	}
	

	private static String createTimestamp()
	{
		DateFormat df = new SimpleDateFormat("dd-MMM-yyyy hh:mm:ss", Locale.UK); 
		df.setTimeZone(TimeZone.getTimeZone("GB"));
		return df.format(new Date());
	}
}


package uk.co.his.test.simpleol;

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;
import java.util.UUID;

import javax.persistence.Basic;
import javax.persistence.CascadeType;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.Entity;
import javax.persistence.EntityManager;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.OneToMany;
import javax.persistence.OrderBy;
import javax.persistence.PostLoad;
import javax.persistence.PostPersist;
import javax.persistence.PreUpdate;
import javax.persistence.Version;



@Entity
@NamedQueries({})
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn
public class Container {

	@Id String id;

    @Basic int dummyProp;
    
    @Version private int version;

	public int getDummyProp() {
		return dummyProp;
	}

	public void setDummyProp(int dummyProp) {
		this.dummyProp = dummyProp;
	}

	public void setUUID() {
		id = UUID.randomUUID().toString();
	}
	
	 @Basic String timestamp;
	    
	    public String getTimestamp() {
			return timestamp;
		}

		public void setTimestamp(String timestamp) {
			this.timestamp = timestamp;
		}
		
	@ManyToOne(fetch=FetchType.LAZY)
	private Singleton singleton;
	
	public void setSingleton(Singleton singleton) {
		this.singleton = singleton;
	}

	@OneToMany(cascade=CascadeType.ALL, mappedBy="container")
	@OrderBy("item_idx")
    java.util.List<Item>  items  = new ArrayList<Item>();
	
	public java.util.List<Item> getItems() {
		return items;
	}

	protected  Item itemsAddNew(Item newObj, EntityManager em) {
	    newObj.setUUID();
	    newObj.setTimestamp(createTimestamp());
	    em.persist(newObj);
	    items.add(newObj);

		em.flush();
	    newObj.setContainer(this);
	    return newObj;
	}
	
	@PreUpdate
    @PostPersist
    public void z_updateIndices() {
		//System.out.println("z_updateIndices " + id + "^" + hashCode() + ", items=" + items.hashCode());
		for (int i = 0; i<items.size();i++) {
			items.get(i).setItemIndex(i);
        }
	}
	
	@PostLoad
	public void postLoad() {
		//System.out.println("PostLoad " + id + "^" + hashCode() + ", items=" + items.hashCode());
		for (int i = 0; i<items.size();i++) {
			//System.out.println("Item at " + i + " is " + items.get(i));
			if(items.get(i) == null) {
				System.err.println("FOUND IT!!!!");
				System.exit(1);
				
			}
        }
	}
	
	private static String createTimestamp()
	{
		DateFormat df = new SimpleDateFormat("dd-MMM-yyyy hh:mm:ss", Locale.UK); 
		df.setTimeZone(TimeZone.getTimeZone("GB"));
		return df.format(new Date());
	}
}

package uk.co.his.test.simpleol;

import java.util.UUID;

import javax.persistence.Basic;
import javax.persistence.DiscriminatorColumn;
import javax.persistence.Entity;
import javax.persistence.FetchType;
import javax.persistence.Id;
import javax.persistence.Inheritance;
import javax.persistence.InheritanceType;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.Version;


@Entity
@NamedQueries({
})
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn
public class Item {

	
	@Id
	private String id;
	
	@Version private int version;

    @Basic
    private int item_idx;
    
    @Basic int creationOrder;
    
    @Basic int dummyProp;
    
    @Basic String timestamp;
    
    public String getTimestamp() {
		return timestamp;
	}

	public void setTimestamp(String timestamp) {
		this.timestamp = timestamp;
	}

	public int getDummyProp() {
		return dummyProp;
	}

	public void setDummyProp(int dummyProp) {
		this.dummyProp = dummyProp;
	}

	public Item(int creationOrder) {
    	this.creationOrder = creationOrder;
    }
    
    private Item() {}
    
	@ManyToOne(fetch=FetchType.LAZY)
    private Container container;
	
	protected void setContainer(Container container) {
		this.container = container;
	}

	public void setUUID() {
		id = UUID.randomUUID().toString();
	}

	public void setItemIndex(int index) {
		item_idx = index;
	}
	
	public String toString() {
		return "Item id=" + id + ", creationOrder=" + creationOrder + ", item_idx=" + item_idx;
	}
}


package uk.co.his.test.simpleol;

import org.eclipse.persistence.descriptors.ClassDescriptor;
import org.eclipse.persistence.descriptors.DescriptorEvent;
import org.eclipse.persistence.descriptors.DescriptorEventAdapter;
import org.eclipse.persistence.descriptors.DescriptorEventManager;
import org.eclipse.persistence.sessions.Session;

public class Customizer implements org.eclipse.persistence.config.SessionCustomizer {
	
	public Customizer()
	{
		System.err.println("The Customizer has been started");
	}

	@Override
	public void customize(Session session) throws Exception {
		System.err.println("Customize a " + session);
		System.err.println("Customize session called " + session.getName());
		for (ClassDescriptor descriptor : session.getDescriptors().values()) {
			if(descriptor.getJavaClass() == Container.class) {
				System.out.println("Found PersonHealth");
				descriptor.getEventManager().addListener(new DescriptorEventAdapter() {

					private void checkObjects(Container source, Container original, String eventName) {
						Container evtObj = original==null?source:original;
						String evtObjStr = evtObj==null?"null":("" + evtObj.dummyProp + "$" + evtObj.id);
						//String info = eventName + ": " + original.dummyProp + "$" + original.id + ". source " + source.dummyProp + "$" + source.id;
						String info = eventName + ": " + evtObjStr;
						System.out.println(info);
						if(original != null) {
							if(original.items.contains(null)) {
								System.out.println("!!!!!!!!! " + info + " original contains null");
							}
						}if(source != null) {
							if(source.items.contains(null)) {
								System.out.println("!!!!!!!!! " + info + " source contains null");
							}
						}
					}
					
					private void processEvent(DescriptorEvent event) {
						checkObjects((Container)event.getSource(), (Container)event.getOriginalObject(), eventCodeToString(event.getEventCode()));
					}
					
					private String eventCodeToString(int eventCode) {
						switch(eventCode) {
						case DescriptorEventManager.PreWriteEvent :
							return "PreWriteEvent";
						case DescriptorEventManager.PostWriteEvent :
							return "PostWriteEvent";
						case DescriptorEventManager.PreDeleteEvent :
							return "PreDeleteEvent";
						case DescriptorEventManager.PostDeleteEvent :
							return "PostDeleteEvent";
						case DescriptorEventManager.PreInsertEvent :
							return "PreInsertEvent";
						case DescriptorEventManager.PostInsertEvent :
							return "PostInsertEvent";
						case DescriptorEventManager.PreUpdateEvent :
							return "PreUpdateEvent";
						case DescriptorEventManager.PostUpdateEvent :
							return "PostUpdateEvent";
						case DescriptorEventManager.PostBuildEvent :
							return "PostBuildEvent";
						case DescriptorEventManager.PostRefreshEvent :
							return "PostRefreshEvent";
						case DescriptorEventManager.PostCloneEvent :
							return "PostCloneEvent";
						case DescriptorEventManager.PostMergeEvent :
							return "PostMergeEvent";
						case DescriptorEventManager.AboutToInsertEvent :
							return "AboutToInsertEvent";
						case DescriptorEventManager.AboutToUpdateEvent :
							return "AboutToUpdateEvent";
						case DescriptorEventManager.AboutToDeleteEvent :
							return "AboutToDeleteEvent";
						case DescriptorEventManager.PrePersistEvent :
							return "PrePersistEvent";
						case DescriptorEventManager.PreRemoveEvent :
							return "PreRemoveEvent";
						case DescriptorEventManager.PreUpdateWithChangesEvent :
							return "PreUpdateWithChangesEvent";
						}
						return "Unknown event";
					}

					@SuppressWarnings("unused")
					@Override
					public void aboutToInsert(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void aboutToUpdate(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void postBuild(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void postClone(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void postMerge(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void postRefresh(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void preInsert(DescriptorEvent event) {
						processEvent(event);
					}

					@SuppressWarnings("unused")
					@Override
					public void preUpdateWithChanges(DescriptorEvent event) {
						processEvent(event);
					}
					
				});
			}
		}
	}

}


persistence.xml;

Code: [Select all] [Show/ hide]
<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://java.sun.com/xml/ns/persistence"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0"
	xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
	

	
	<persistence-unit name="TestSimpleOrderedLists_memPU">
		<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
		<class> uk.co.his.test.simpleol.Singleton</class>
		<class> uk.co.his.test.simpleol.Container</class>
		<class> uk.co.his.test.simpleol.Item</class>
		<properties>
			<property name="eclipselink.target-database" value="org.eclipse.persistence.platform.database.H2Platform"/>
			<property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:TestSimpleOrderedListsmem"/>
			<property name="eclipselink.ddl-generation" value="create-tables"/>
			<property name="eclipselink.session.customizer" value="uk.co.his.test.simpleol.Customizer"/>
		</properties>
	</persistence-unit>

</persistence>


I have reimplemented this using @OrderColumn and have the same problems...


When I run the uploaded files I get the following output

The Customizer has been started
Customize a ServerSession(
	DatabaseAccessor(disconnected)
	H2Platform)
Customize session called TestSimpleOrderedLists2_memPU
Found Container
[EL Info]: 2011-10-19 20:05:53.627--ServerSession(33341602)--EclipseLink, version: Eclipse Persistence Services - 2.4.0.v20110824-r9956
[EL Info]: 2011-10-19 20:05:53.782--ServerSession(33341602)--TestSimpleOrderedLists2_memPU login successful
1: Commit it!
PreInsertEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
PreInsertEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
AboutToInsertEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
AboutToInsertEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
PostMergeEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
PostMergeEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
1: Committed!
PostCloneEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
PostCloneEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
PreUpdateWithChangesEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
PreUpdateWithChangesEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
2: Commit it!
PostMergeEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
PostMergeEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
2: Committed!
PostCloneEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
PostCloneEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
........3: Commit it!
3: Committed!
PostCloneEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
PostCloneEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
PreUpdateWithChangesEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
Inserted One Item
PreUpdateWithChangesEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
Inserted One Item
PreUpdateWithChangesEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
Inserted One Item
PreUpdateWithChangesEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
Inserted One Item
4: Commit it!
PostMergeEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
!!!!!!!!! PostMergeEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d source contains null
PostMergeEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
4: Committed!
PostCloneEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d
!!!!!!!!! PostCloneEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d original contains null
!!!!!!!!! PostCloneEvent: 1$045a6045-18fd-4293-89b6-f7a9177d0a2d source contains null
PostCloneEvent: 2$2481696d-f758-4c17-94cd-4e39f37e9b47
.......Found it!!!

Here is the persistence.xml



<persistence-unit name="TestSimpleOrderedLists2_memPU">
		<provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
		<class> uk.co.his.test.simpleol2.Singleton</class>
		<class> uk.co.his.test.simpleol2.Container</class>
		<class> uk.co.his.test.simpleol2.Item</class>
		<properties>
			<property name="eclipselink.target-database" value="org.eclipse.persistence.platform.database.H2Platform"/>
			<property name="javax.persistence.jdbc.url" value="jdbc:h2:mem:TestSimpleOrderedLists2mem"/>
			<property name="eclipselink.ddl-generation" value="create-tables"/>
			<property name="eclipselink.session.customizer" value="uk.co.his.test.simpleol2.Customizer"/>
			
			<!-- 
			<property name="eclipselink.logging.level" value="FINE" />
			<property name="eclipselink.logging.session" value="true" />
			-->
			
		</properties>
	</persistence-unit>