Hi, I'm fairly new to hibernate, but am working on an existing app. I'm using hibernate in an Apache Axis web service.

I have a class A, which is associated with another class location. Location is abstract, sometimes instantiated as a point, sometimes a line. So, my program creates an object of type A and associates it with a point or a line and then does a saveOrUpdate on class A. I can go and check the database and see that all entries are there as expected, with the correct ids and attributes. But when I attempt to retrieve the object A, i get an exception:

- Error performing load command
org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: Location

Now here's the strange part. I have my tester program (test) set up to create an object associated with a point or a line, depending on the command line parameter sent in. So if i say

test point

it creates the object and associates it with a point.

test line

creates the object and associates it with a line.

I am finding that the first time I run it, there are no exceptions. Then I can run "test point" repeatedly and be successful, but when I switch to running "test line", I get the exception mentioned above.

If I restart the web service (all the hibernate code is in the web service), "test line" works again. It's somewhat unpredictable when I will see this exception, but one thing is consistent. If I restart the web service, the next time I run the program, there is no problem.

Each call to add the object to the database and to pull it out are separate sessions and transactions.

Any ideas?

Can you provide your mappings and code wich accesses objects?