Hi all,

is it possible to mix inheritance strategies?
My concrete example is:

ContentItem <-- FileItem <-- ImageItem

These three classes are supposed to be base classes for other (maybe more specialized classes) in a CMS.

Now, for performance sake these three classes would be part of a table per class hierarchy scenario, putting all properties into fields of one table.
This table would be part of the CMS Core.

Others might want to derive from one of these three classes and add additional properties etc. Could this then be solved using joined subclasses?

For example, taken the FileItem class from above, in a CMS-module I want a XslFileItem, derived from FileItem - could this be done?

Thanks for any help!

I don't have a link handy, but no, I don't believe this is supported by NHibernate 1.x. The feature was added at Hibernate 3.x, but NH is a port of the 2.1.x version. Nor are there plans to add it before the Great Porting Project (of H3 to NH).

We rolled our own framework to do this. We keep a type registry (dictionary), keyed by the entity's unqualified class name. Each registry entry is itself an inheritance list; the last item in the list is the type actually instantiated. Each type in a given inheritance list for an entity must have the same unqualified class name, but uses a different namespace (and normally a different assembly). Our implementation of NHibernate.IInterceptor.Instantiate uses the type registry to instantiate the correct type. Also, the hbm.xml file for the last type in each inheritance list is added to the NHibernate configuration. This way, existing HQL queries (that don't specify namespaces) work without modification, automagically returning the correct subtypes.

Does this approach solve your problem?

Thanks for your help.

I am not sure if the mentioned "type registry" would work with what I wanted to do.

If mixing won't work, I guess I will have to stick with "joined subclass" approach.