Using NHibernate Collection Filters with DDD collections

Question

I am trying to map a domain model in NHibernate. The domain model is implemented with what I think is DDD style. The mapping works mostly but then when I try to use a collection filter on an a collection I get an exception which says: The collection was unreferenced.

I know the problem comes from how I've implemented the collection. My question: Is it possible to use collection filters in nHibernate on collections implemented this way or should I just forget it, ie nHibernate cannot work with this.

The code is as follows:

Person
{
   IList<Address> _addresses = new List<Address>();
   public string FirstName {get; set;}
   ...
   public void addAddress(Address address)
   {
      // ... do some checks or validation
      _addresses.Add(address);
   }

   public void removeAddress(Address address) {...}

   public ReadOnlyCollection<Address> Addresses 
   { 
      get { return new ReadOnlyCollection<Address>(_addresses); }
   }
}

The main issue is that I don't want to expose the internal addresses collection publicly. Every other thing works, I use the field.camelcase-underscore access so nHibernate interacts directly with the field. I've been working through the Hibernate in Action book, an now I'm in chapter 7 where it deals with collection filters.

Is there any way around this. I've got it to work by exposing the internal collection like this:

public ReadOnlyCollection<Address> Addresses 
{ 
   get { return _addresses; }
}

but I really dont want to do this.

Help would really be appreciated.

Jide

Answer 1

If I recall correctly - NHibernate filter works as additional clause in sql queries to reduce returned rows from db.

My question to You is - why do You need that?
I mean - how much addresses one person might have? 1? 5? 10?

---

About collection isolation...

I myself just accept it as a sacrifice for NHibernate (just like argument-less ctor's and "virtual`ity") and use exposed IList everywhere (with private setters) just to reduce technical complexity. Their contents surely can be modified from outside, but I just don't do that.

It's more important to keep code easily understandable than making it super safe. Safety will follow.