NHibernate add unmapped column in interceptor

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

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.

Answer 2

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 3

Ive added a post on my blog outlining how this all works for anyone who hits this problem http://www.dav-evans.com/?p=75