WrongClassException when doing session.merge()

Hibernate ORM
1

Our lifecycle is, I believe, pretty common. We fetch objects from the database, serialize them to JSON and let client-side Javascript unpack it and fill in a form so our users can make changes. The data comes back and is loaded as Java objects by Struts. We re-fetch the original object from Hibernate and do a merge to update with new values.

We have a class, TargetProductGroup. It has a field of type BasicModel. BasicModel in turn has two subclasses, SlagModel and MgOSatModel. In this particular test case, the TargetProductGroup has a MgOSatModel. When we try to call merge, we get this exception:

WrongClassException: Object was not of the specified subclass [BasicModel]: class of the given object did not match class of persistent copy

We do check in the code that the local copy we get from session.find() has an MgOSatModel.

2

What Hibernate version do you use? Did you try updating to the latest version yet and see if that problem persists?

3

Sorry to have wasted your time. The actual problem was the reverse - our stupid web framework gave us a BasicModel, which of course can’t be merged with the MgOSatModel in the database …