The good news is that Hibernate Envers works as expected - versions (entries into the AUD tables) are not created unless an auditable property is modified.
However, in our application we had implemented a MergeEventListener which was updating tracking fields (lastUpdated, lastUpdatedBy) on every entity save. This caused Envers to make a new version even when there were no changes to the entity.
The solution was quite simple in the end (for us) - using an example of how to use Interceptors and Events from Hibernate: http://docs.jboss.org/hibernate/core/3.6/reference/en-US/html/events.html
We replaced our class implementing PersistEventListener and MergeEventListener with a class that extends EmptyInterceptor and overrides the onFlushDirty and onSave methods.
public class EntitySaveInterceptor extends EmptyInterceptor {
@Override
public boolean onFlushDirty(Object entity, Serializable id, Object[] currentState, Object[] previousState, String[] propertyNames, Type[] types) {
setModificationTrackerProperties(entity);
return super.onFlushDirty(entity, id, currentState, previousState, propertyNames, types);
}
@Override
public boolean onSave(Object entity, Serializable id, Object[] state, String[] propertyNames, Type[] types) {
setModificationTrackerProperties(entity);
return super.onSave(entity, id, state, propertyNames, types);
}
private void setModificationTrackerProperties(Object object) {
if (SecurityContextHolder.getContext() != null && SecurityContextHolder.getContext().getAuthentication() != null) {
Object principal = SecurityContextHolder.getContext().getAuthentication().getPrincipal();
if (principal != null && principal instanceof MyApplicationUserDetails) {
User user = ((MyApplicationUserDetails) principal).getUser();
if (object instanceof ModificationTracker && user != null) {
ModificationTracker entity = (ModificationTracker) object;
Date currentDateTime = new Date();
if (entity.getCreatedDate() == null) {
entity.setCreatedDate(currentDateTime);
}
if (entity.getCreatedBy() == null) {
entity.setCreatedBy(user);
}
entity.setLastUpdated(currentDateTime);
entity.setLastUpdatedBy(user);
}
}
}
}
}
Hooking up the EntitySaveInterceptor to the Hibernate JPA persistence unit
<?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="myapplication" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<properties>
<property name="hibernate.ejb.interceptor" value="org.myapplication.interceptor.EntitySaveInterceptor" />
<property name="hibernate.hbm2ddl.auto" value="none"/>
<property name="hibernate.show_sql" value="false"/>
</properties>
</persistence-unit>
</persistence>
And for completeness, here is the ModificationTracker interface:
public interface ModificationTracker {
public Date getLastUpdated();
public Date getCreatedDate();
public User getCreatedBy();
public User getLastUpdatedBy();
public void setLastUpdated(Date lastUpdated);
public void setCreatedDate(Date createdDate);
public void setCreatedBy(User createdBy);
public void setLastUpdatedBy(User lastUpdatedBy);
}
It should also be possible to solve this problem by using an implementation of PreUpdateEventListener to set the ModificationTracker values because that listener is also only fired when the object is dirty.
