I'm trying to save a domain object with a custom type for its Id, a class called Id that wraps an Int32. I'm trying to use the native generator but when I try to save a new object, I get the following exception...

InvalidCastException: Invalid cast from 'System.Decimal' to 'Project.DataTypes.Id'.]

This is on line 93 of IdentifierGeneratorFactory.cs:

return Convert.ChangeType( identityValue, clazz );

Note that I am working with the most recent NHibernate trunk code updated from the SVN repository as of this morning. My DB engine is MS SqlExpress and hence the reason its getting a decimal for the Identity. I tried adding an explicit and implicit cast operation on my class from decimal to Id but that didn't change anything. I used Reflector to look at the source code for Convert.ChangeType and that looks like its all based on the IConvertable interface and so I'm kinda stuck there.

I'm guessing that I will need to make a custom generator for my custom type. I would still like to use the database generated identifier though. I see the interface IIdentifierGenerator which I assume I need implement but this is where I'm lost and kinda wading through the code trying to figure out what to do next.

<id name="Id" column="ID" unsaved-value="0" type="Project.Persistence.NHibernateTypes.IdType, Project.Persistence">
<generator class="native" />
</id>

I know I can replace "native" with a custom type but writing this type is where I'm struggling. Some pointers would be helpful if anyone has done this.

Looking into the NHibernate code a little further, I think I have found a bug, reported as http://jira.nhibernate.org/browse/NH-621 and added a patch.