Hi,

I have a participant table that I mapped. Everything worked fine till this point when I decided to try the merge().

I have a webpage that allows me to modify a Participant entity. As is normal only a limited number of fields from Participant are going to be edit enabled.

So, when I click submit I endup having an incomplete Participant and I want to merge it with the persisted instance.

Participant has some fields declared as not null as below

<property name="paxStatus" type="string">
<column name="pax_status" length="9" not-null="true" />
</property>

When I did the merge I get this error...

2006-04-13 01:46:08,921 ERROR org.hibernate.PropertyValueException: not-null property references a null or transient value: com.xyz.Participant.paxStatus

The error is normal for a saveUpdate but I thought this case should be managed by merge()...


To me seems that it copies over the null value from the web object

at org.hibernate.engine.Nullability.checkNullability(Nullability.java:72)
at org.hibernate.event.def.DefaultFlushEntityEventListener.scheduleUpdate(DefaultFlushEntityEventListener.java:256)
at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:114)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:195)
at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:76)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:26)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:985)
at com.xyz.HibernateSessionInterceptor.invoke(HibernateSessionInterceptor.java:70)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:144)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:174)


What do you think ?
Q

Is it a must to have a version in my mapping ?

<version name="version" column="VERSION" type="java.lang.Long" />

That implies that I have to persist this to database too ?

From documentation...looks like a recommandation though..

"We very strongly recommend that you use version/timestamp columns for optimistic locking with Hibernate.
This is the optimal strategy with respect to performance and is the only strategy that correctly handles modifications
made to detached instances (ie. when Session.merge() is used)."

The idea of merge is that it takes a POJO and updates all of the mapped properties and updates the database. Hibernate knows nothing of your UI, and merge doesn't allow you to specify that only a few properties should be considered. It can't tell that a null value in a mapped property means that this should not be written to the database. In addition, how would it tell the difference between a property that is null because it wasn't copied from the UI, versus a property that is null because the UI set it null from an empty field. In order to get the merge to work in this case, you will probably have to retrieve a participant from the database, then update any properties from UI fields, and send the resulting fully-populated participant back to the merge.

But then what's the difference between saveOrUpdate and merge();
I really don't see why one would use merge over saveOrUpdate - I will re-read what they say about merge()...

Basically you're saying that prior to merge to do a load myself and overwrite only those fields that I'm capturing from the web. Well, this was the backup plan hoping that merge will merge indeed the values that are not null with the already persitsted entity.

So it doensn't do that...


Q

Urrr...is the NHibernate related? Sounds like Hibernate 3.0 features to me...or are we starting to see these in NHibernate?

True! Wrong forum - I did a search and then I replied!

Merge is part of the new java persistence API, while saveOrUpdate is Hibernate-specific. Both appear to work for disconnected entities, but I have found advantages to merge in the area of collections. Lets say you have a
class Person {
private List phones = new ArrayList();...

Hibernate replaces the ArrayList with a PersistentBag when a Person is loaded from the database.

OK, so who cares?

Well, what if you're serializing the Person and passing it on to some VM that doesn't have the Hibernate library?

I have such a case with my web services. The client doesn't have Hibernate, so a Person passed to the client will only have an ArrayList. Then, it passes it back to the server to be saved. If the client has changed a phone, both merge and saveOrUpdate work. But if the client deleted a phone, saveOrUpdate won't delete it from the database, even if the mapping cascade included delete-orphan. Merge, however, will properly delete it.

But ... I noticed that if a new phone (with no id) is added to the client, merge will not work while saveOrUpdate will correctly create the new phone entry. How do you solve this problem using merge?