Hi Reece,

The original design for fetch plans comes from JDO, where you can specify both fields to load and fields to unload (setting their Java value to null) before serializing them.

So the only impact of an unloaded field is to write null to the output stream.

I'm not sure whether the unload fields ever made it into a JIRA for OpenJPA. You can see some of the dialog here: http://www.mail-archive.com/open-jpa-dev@incubator.apache.org/msg01663.html

It seems to me that adding the ability to specify that fields should be unloaded would address your requirement quite well.


On Mar 11, 2008, at 3:57 PM, Reece Garrett wrote:

Greetings all,
I am trying to do some intelligent serialization of my persistence capable classes. By intelligent I mean that only fields that were in an active fetchgroup during retrieval should be serialized (whether they are null or not). 
Currently I am storing a transient list of properties that should be serialized in the model objects themselves. After retrieving the object I populate the list by inspecting the fetchgroups that were used for the retrieval. The list is then used by xsteam to determing if a property of the object should be serialized. It is working but it's neither pretty nor performant. Ideally, I want each active fetchgroup to fire a postload event and a callback receive a reference to the object being retrieved and a reference to the fetchgroup that generated the event. I could then inspect the fetchgroup attributes and populate my list. Unfortunately, the callback only gets a reference to the object being retrieved so I cannot figure out which properties were loaded.
Any insite is much appreciated.

Craig Russell

Architect, Sun Java Enterprise System http://java.sun.com/products/jdo

408 276-5638 mailto:Craig.Russell@sun.com

P.S. A good JDO? O, Gasp!