Hi Pierre! When you use nested contexts (http://cayenne.apache.org/doc/nested-datacontexts.html), you don't need to manually copy objects between contexts, it collapses to just calling one method. I think that's exactly what you need.
Manually calling setObjectContext (and even worse, deprecated setDataContext), by my experience, usually results in errors since Cayenne's internal object graph isn't properly updated. Andrey
