(Fluent). NHibernate mapping: use IUserType to map custom foo class - if boo.foo.Id is 0 then write to DB: boo.foo = NULL

I have the following construction:

class Person {
 int Id;
 Foo fooObject;
}

class Foo {
 int Id;
 //some more properties - doesn't matter
}

      

        
        
        
      

    

The database for this example is pretty simple;

Person table (int Id, int foo_Id)
Foo table (int Id, some more properties ...)

I often end up with a Person object that contains an initialized Foo object that has no value (for example, Id is 0). In this case, I want to store NULL in the Person.foo_Id database field.

I guess I should be using IUserType for such a conversion, but I just don't know how I should implement this with a custom Foo class ... Anyone have any experience with this topic? By the way, I am using FluentNHibernate.

Thanks in advance!