Is it possible to map two classes (baseclass and subclass) to a single table without the use of a discriminator? if I only have one subclass type, then every record in the table is of type base class and subclass. I need to be able to do this, as the subclass is a very large entity, and the baseclass is very small. I don't always want to be getting the large subclass. I've tried doing this as a mapping file with two classes, but whether I try to get the base type or the subclass type, NHibernate issues two select statments - one for the base class and one for the subclass. When I call List, I end up with a list of every base class and also the same identity in the form of the subclass.

Is this possible? If it's not possible to do this without a discriminator, if I add a discriminator column won't all rows in the table end up with the same value given they are all of both types?

The statement "the object is of both types" is a non-concept in the OO idiom. If you really an object to function "differently" in a different context, the pattern you are looking for is a role.

However, in your case It looks like you need lazy-loaded properties (which is not currently supported) and built this "inheritance" model as a hack to get similar functionality. So, you really have only one class (the subclass), it's just that you only need to load a subset of the properties most of the time, so you devised a "base" as a container for those properties.

Lazy properties are a very useful feature that isn't easily supported by NH. As far as I know, the only recognized method involves supplying your own ProxyFactory and LazyInitializer, which seems quite advanced (probably more info on Ayende Rahien's blog).

I'd also put up another post here to see what workarounds the community has developed to "spoof" this missing feature.

I had the same question but came up with a workaround. I couldn't get it to work as a true subclass, so I created a new hbm with a one-to-one relationship to the object that I was trying to extend.

I did something like this:





Then in your "subclass" you can use decorator methods to access the properties of your "base" class.




A little hacky but it had the effect that I was trying to acheive :)