Re: [eclipselink-users] How to compare entities from two different datab

[James Sutherland <jamesssss@xxxxxxxxx>]

There is no public API for this.  You could call down to the ObjectBuilder
and call the merge with your two objects directly.



saasira wrote:
> 
> Thanks James for those useful tips; this API has helped me a lot.
> 
> I think this eclipselink's change set API needs more civerage in the wiki
> so
> that other guys can benefit from it.
> 
> It is also useful for audit logging purposes where just the changes made
> to
> the entity, but not the entire entity, needs to be logged.
> 
> 
> By the way, I would like know if there is any way to merge entities based
> on
> the object equality instead of the primary key equality;
> the reason being that when we compare entities from two data bases, most
> of
> the times, the primary keys (pseudo identities, usually numbers for easy
> mapping of references) will be different where as logically the entities
> are
> same based on some unique field(s).
> 
> So, we had to selectively compare the unique fields for logical equality
> and
> then selectively copy all the fields from one entity of reference database
> to the other entity of the comparing database, carefully avoiding the copy
> of primary key. It would be very helpful, if there is any option to ask
> eclpselink to merge by logical equality rather than primary key equlity.
> 
> Can you guys let me know if this is possible with eclipselink?
> 
> Thanks and Regards,
> Samba
> 
> 
> On Wed, Apr 7, 2010 at 5:59 AM, James Sutherland
> <jamesssss@xxxxxxxxx>wrote:
> 
>>
>> Assuming the objects have the same primary keys, you could read from one
>> and
>> call merge() into the other.  This would merge any changes, or do nothing
>> if
>> no changes.
>>
>> There is a compareObjects() method on AbstractSession that will compare
>> two
>> objects and return if they match.
>>
>> If you get the UnitOfWork after merging you can get the
>> UnitOfWorkChangeSet
>> that contains the set of changes.
>>
>> There is also a compareForChange() method on ObjectBuilder that will
>> compare
>> two objects and build an ObjectChangeSet.
>>
>> Doing this for an entire database may take a while depending on the
>> database
>> size.  You may be better off using lower level database utilities, or
>> just
>> drop the test db, and clone the reference.
>>
>>
>> saasira wrote:
>> >
>> > Hi all,
>> >
>> >     I need to compare data in two databases, one a test db and the
>> other
>> > being reference db, and then patch the differences in the database that
>> is
>> > being compared from the
>> >     data in the reference db.
>> >
>> >     Can eclipselink detect changes between two entities, each loaded by
>> > a different entity manager?
>> >
>> >     Can I use the eclipselink change tracking api ( merge the
>> comparable
>> > entity with reference entity manager and then invoke UnitOfWork.
>> > getUnitOfWorkChangeSet() or
>> >     UnitOfWork.getCurrentChanges() ) for finding the differences
>> between
>> > the
>> > test entity and the reference enitity?
>> >
>> >
>> >    I'm open to any other approach that can help me achieve this; even
>> > hibernate or openjpa is also ok to me!
>> >
>> > Thanks and Regards,
>> > Samba
>> >
> 
> 


-----
http://wiki.eclipse.org/User:James.sutherland.oracle.com James Sutherland 
http://www.eclipse.org/eclipselink/
 EclipseLink ,  http://www.oracle.com/technology/products/ias/toplink/
TopLink 
Wiki:  http://wiki.eclipse.org/EclipseLink EclipseLink , 
http://wiki.oracle.com/page/TopLink TopLink 
Forums:  http://forums.oracle.com/forums/forum.jspa?forumID=48 TopLink , 
http://www.nabble.com/EclipseLink-f26430.html EclipseLink 
Book:  http://en.wikibooks.org/wiki/Java_Persistence Java Persistence 
-- 
View this message in context: http://old.nabble.com/How-to-compare-entities-from-two-different-databases-and-replace-one-with-the-other--tp28094979p28287882.html
Sent from the EclipseLink - Users mailing list archive at Nabble.com.