how to get OneToMany relationship revision in Hibernate envers - hibernate-envers

Question

we have two entities like Resource and NonFTECost. And we have relationship between these is OneToMany bi-directional. below is the entities
#Getter
#Setter
#NoArgsConstructor
#Entity
#Table
public class Resource {
#NotNull
#Column(name = "NAME", nullable = false, length = 255)
#Audited(withModifiedFlag = true)
private String name;
#OneToMany(mappedBy = "resource", cascade = CascadeType.PERSIST, fetch = FetchType.LAZY)
#Audited
private List<NonFTECost> costings = new ArrayList<>();
//other fields
}
#Getter
#Setter
#Table
#Entity
public class NonFTECost {
#NotNull
#Audited(withModifiedFlag = true, modifiedColumnName = "PAYMENT_MOD")
private Payment payment;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "RESOURCE_CODE", nullable = false, foreignKey = #ForeignKey(name = FK_COST_DETAILS_RESOURCE_CODE))
#Audited(withModifiedFlag = true, modifiedColumnName = "RESOURCE_CODE_MOD", targetAuditMode = RelationTargetAuditMode.AUDITED)
private Resource resource;
//other fields
}
now i create the one resource wiht costings, then it will create new revision for each audit table. And then i changed only payment field of NonFTECost entity, it will create new revision in NonFTECost_Aud table(it is also the part of resource update).
Question:- While getting the revision of resource, i want to get revisions of NonFTECost for that perticular resource entity. because of i want to show to user like fieldName oldvalue newvalue
Please help me to sort out the issue.

Answer 1

You should be able to fetch the associated NonFTECost entities for a given revision of Resource by iterating that collection on the specific revision instance you queried.
For example, lets say I was interested in revision 5 of Resource
final Number revision = 5;
final AuditReader auditReader = auditReaderFactory.get( session );
final Resource resource = auditReader.find( Resource.class, resourceId, revision );
for ( Cost cost : resource.getCosts() ) {
// do whatever with cost
}
Now what you need is how to take that Cost instance and find out what changed. Since you use the feature withModifiedFlags=true, this allows us to make special use of forRevisionsOfEntityWithChanges.
The one thing I want to point out is that it is possible in your mapping scenario that a NonFTECost entity could have a higher revision than that of your Resource if you happen to modify the cost entity in a transaction where no modification happens specifically to Resource .
With that in mind, you'll need to account for that in the for-loop logic. So inside that loop, we'll need to execute a query based on the Cost instance and fetch its revision history separately.
// This list is an object array that contains the following
// Index 0 - The `Cost` entity again at the revision
// Index 1 - The revision entity (contains revision number/timestamp)
// Index 2 - The RevisionType: ADD, MOD, or DEL
// Index 3 - Set<String> of property names that changed at this revision
List results = auditReader.createQuery()
.forRevisionsOfEntityWithChanges( Cost.class, false )
.add( AuditEntity.id().eq( cost.getId() ) )
.addOrder( AuditEntity.revisionNumber().desc() )
.setMaxResult( 2 )
.getResultList();
If the results list only contains 1 row, then you know a couple of things (assuming no data pruning)
index 2 should be RevisionType.ADD
Index 3 contains Set<String> of fields set during the original persist.
There are no fields that have an old value, just whatever their insert persist value was.
If the results list contains 2 rows, then this is where you'll need to handle old and new value logic. You should be able to do something like this:
if ( results.size() == 2 ) {
Object[] newArray = (Object[]) results.get( 0 );
Object[] oldArray = (Object[]) results.get( 1 );
Set<String> propertiesChanged = (Set<String>) newArray[3];
for ( String propertyName : propertiesChanged ) {
if ( "value".equals( propertyName ) ) {
Double newValue = ( (NonFTECost) newArray[0] ).getValue();
Double oldValue = ( (NonFTECost) oldArray[1] ).getValue();
}
}
}
else if ( results.size() == 1 ) {
Object[] array = (Object[]) results.get( 0 );
Set<String> propertiesChangedOnInsert = (Set<String>) array[3];
// do whatever here
}
This isn't the most elegant of solutions, but it works.