NHibernate add unmapped column in interceptor - nhibernate

Question

I'm trying to save a mapped entity using NHibernate but my insert to the database fails because the underlying table has a column that does not allow nulls and IS NOT mapped in my domain object. The reason it isn't mapped is because the column in question supports a legacy application and has no relevance to my application - so I'd like to not pollute my entity with the legacy property.
I know I could use a private field inside my class - but this still feels nasty to me. I've read that I can use an NHibernate interceptor and override the OnSave() method to add in the new column right before my entity is saved. This is proving difficult since I can't work out how to add an instance of Nhibernate.type.IType to the types parameter of my interceptor's OnSave.
My Entity roughly looks like this:
public class Client
{
public virtual int Id { get; set; }
public virtual int ParentId { get; set; }
public virtual string Name { get; set; }
public virtual string Phone { get; set; }
public virtual string Email { get; set; }
public virtual string Url { get; set; }
}
And my interceptor
public class ClientInterceptor : EmptyInterceptor
{
public override bool OnSave(object entity, object id, object[] state, string[] propertyNames, NHibernate.Type.IType[] types)
{
if (entity is Client)
{
/*
manually add the COM_HOLD column to the Client entity
*/
List<string> pn_list = propertyNames.ToList();
pn_list.Add("COM_HOLD");
propertyNames = pn_list.ToArray();
List<Object> _state = state.ToList();
_state.Add(false);
state = _state.ToArray();
//somehow add an IType to types param ??
}
return base.OnSave(entity, id, state, propertyNames, types);
}
}
Does anyone have any ideas on how to do this properly?

Answer 1

I can't say for sure since I've never actually done this (like Stefan, I also prefer to just add a private property), but can you just add a NHibernate.Type.BooleanType to the types array?
List<IType> typeList = types.ToList();
typeList.Add(new BooleanType());
types = typesList.ToArray();
EDIT
Yes, it looks like you are right; the types have an internal constructor. I did some digging and found TypeFactory:
Applications should use static
methods and constants on
NHibernate.NHibernateUtil if the
default IType is good enough. For example, the TypeFactory should only
be used when the String needs to have a length of 300 instead of 255. At this point
NHibernate.String does not get you thecorrect IType. Instead use TypeFactory.GetString(300) and keep a
local variable that holds a reference to the IType.
So it looks like what you want is NHibernateUtil:
Provides access to the full range of
NHibernate built-in types. IType
instances may be used to bind values
to query parameters. Also a factory
for new Blobs and Clobs.
typeList.Add(NHibernateUtil.Boolean);

Answer 2

Personally I wouldn't do it so complicated. I would add the private property and assign it a default value - finished. You could also consider a default value in the database, then you don't need to do anything else.
private virtual bool COM_HOLD
{
get { return false; }
set { /* make NH happy */ }
}
Before writing a interceptor for that I would consider to write a database trigger. Because with the Interceptor you are "polluting" your data access layer. It could make it unstable and you could have strange problems.