NHibernate.Mapping.Attributes.JoinedSubclass usage

gene · **Posted:** Sat Nov 19, 2005 3:19 am

I have gone through the tutorial, and have implemented attributes in my code. In one place, it struck me odd that I had to add attributes to the properties of the class, rather than to the class itself. For example:

Code:

[NHibernate.Mapping.Attributes.JoinedSubclass(NameType=typeof(Subclass), ExtendsType=typeof(SomeClass), Table="MyTable", Lazy=true)]
public class Subclass: SomeClass
{
   [NHibernate.Mapping.Attributes.Key(-1, Column="key" )]
   private string prop;
   [Nhibernate.Mapping.Attributes.Property]
   public string Prop
   {
      get { return prop; }
      set { prop = value; }
   }
}

It seems like Key should be specified right after JoinedSubclass, rather than inside the class. Also, I was wondering why the JoinedSubclass does not get emitted into the XML as a child of the appropriate class element, but rather as a sibbling, with the (as a result) required "extends" attribute.

Thanks for the neat tools!

Gene

KPixel · **Posted:** Sat Nov 19, 2005 9:56 am

NHibernate.Mapping.Attributes behavior is hevily influenced by the XML representation of the mapping.

[Key] is a property/field attribute because <key> is a sub-element of <joined-subclass>.
This design was choosed because it allowed me to write a generator which means that all mapping are available and the maintenance cost is very low.

And the JoinedSubclass will be in its Class parent mapping only if you put it in the class body. Eg:

Code:

[Class] class BaseClass
{
    [JoinedSubclass] class ChildClass
    {}
}

Note that NHibernate.Mapping.Attributes doesn't try to be too smart: Here, ChildClass will be in BaseClass mapping and as "Extends" is not set, NHibernate will assume that ChildClass inherits from BaseClass...