Hi,

I've written a small proof-of-concept app for us using NHibernate in a new project, but there's one issue I can't resolve.

The test model is that we have an Employee base class, extended by others such as Engineer, Director, Cleaner etc.

For various reasons, we only want to persist the Employee class (with any other role-specific detail being stored in an xml field in Employee).

So, we have the following:
- SQL Server 2005 table "Employee"
- Employee.hbm.xml mapping file
- Employee Class and additional aforementioned sub-classes.

The Session.Save() method is in the Employee Class.

When we try to persist an instance of Employee, it works perfectly, as expected.

However, if we want to persist a Director, we get the message:

"MappingException was unhandled"
"Unknown entity class: testapp1.Director"

Which sort of makes sense, because we haven't written a mapping file for the Director, just the Employee. But we just want to persist it as an Employee.

We tried doing .Save( (Employee)director) but still get the same exception.

Can anyone explain how this should be done?

Any help much appreciated

Artie

Hi Artie,

I think you'll need to add a subclass element to your mapping, just without any extra properties for the subclass.

Regards,
Richard

Thanks for your response, Richard.

One of the reasons we had used the single Employee class for persistance was so that we only had to configure that class in the database and hbm file.

We wanted to be able to hide the fact that the other Employee sub-classes would also be getting persisted VIA the Employee persistance, and didn't want to refer to each of these classes in the hbm file.

Is there another way of doing this?

Artie

Hi Artie,



If NHibernate isn't told about the extra classes then I don't think it can create them or persist them (understandably).

What are the concerns with referring to the sub-classes in the mapping file?

Other than that, you could try removing the subclassing, and replace it with a state/strategy pattern, but it sounds like more work than simply specifying the classes in the mapping.

Regards,
Richard