[hibernate-issues] [Hibernate-JIRA] Commented: (HHH-3030) NullPointerException happens in versioning

[Rishik Dhar (JIRA)]

    [ http://opensource.atlassian.com/projects/hibernate/browse/HHH-3030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_30414 ] 

Rishik Dhar commented on HHH-3030:
----------------------------------

Prashant,

What you have done is stopped using the feature of "version" which is used for optimistic locking at the object level in case of concurrent update on a persistent object in the ORM session level cache.

By removing the version field, the entity will no longer be managed by the Hibernate for optimistic locking and will lead to corruption of the state of data in your application. The change you have made may be okay if a concurrent modification of a persistent object never happens in your application, i.e. an object is always accessed sequentially by different transactions within the current session. 

However, consider this case, if there are two parallel transactions that need to perform a read-write operation on the same object, and both of them read the object simultaneously and update the object, then you transactions will simply ignore the changes made by the other transaction and try to commit their changes and end up corrupting the state of the data.

For more information read here: http://www.redhat.com/docs/manuals/jboss/jboss-eap-4.3/doc/hibernate/Hibernate_Reference_Guide/Transactions_And_Concurrency-Optimistic_concurrency_control.html

You may want to read this before making the change permanent. The only thing that you need to take care of if you decide to retain the version feature will be introduce the version column in your tables and set the default value as 0 for the respective entities mapped with the version property defined in the HBM.

> NullPointerException happens in versioning
> ------------------------------------------
>
>                 Key: HHH-3030
>                 URL: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3030
>             Project: Hibernate3
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 3.2.5
>         Environment: any
>            Reporter: John
>            Priority: Minor
>
> Here is the stack trace:
> java.lang.NullPointerException
> 	at org.hibernate.type.IntegerType.next(IntegerType.java:59)
> 	at org.hibernate.engine.Versioning.increment(Versioning.java:25)
> 	at org.hibernate.event.def.DefaultFlushEntityEventListener.getNextVersion(DefaultFlushEntityEventListener.java:358)
> 	at org.hibernate.event.def.DefaultFlushEntityEventListener.scheduleUpdate(DefaultFlushEntityEventListener.java:250)
> 	at org.hibernate.event.def.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:121)
> 	at org.hibernate.event.def.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:196)
> 	at org.hibernate.event.def.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:76)
> 	at org.hibernate.event.def.DefaultAutoFlushEventListener.onAutoFlush(DefaultAutoFlushEventListener.java:35)
> 	at org.hibernate.impl.SessionImpl.autoFlushIfRequired(SessionImpl.java:969)
> 	at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1114)
> 	at org.hibernate.impl.QueryImpl.list(QueryImpl.java:79)
>         ......
> The code is:
> 	public Object next(Object current, SessionImplementor session) {
> 		return new Integer( ( (Integer) current ).intValue() + 1 );
> 	}
> Should there be a null checking for the object "current"?

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