Adding methods to NHibernate domain model collections

rbirkby · **Joined:** Fri Apr 03, 2009 10:36 am **Posts:** 6

I've been building an NHibernate domain model from our legacy database for a few days now, building out the domain model with methods - I hate anemic domain models.

But I've yet to work out how to add methods to ISet or Collection class instances created by NHibernate.

We have a legacy handbuilt domain model which would be nice to replace with NHibernate and the collection classes have methods such as Merge() or properties like AllSuccessful. How do I give the NHibernate domain model the same domain methods?

Thanks,
Richard
ps I'd rather not hear any answer containing the phrase "Extension Method"...

wolli · **Posted:** Fri Apr 03, 2009 12:49 pm

You can wrap the hibernate collections in a component which represents your enhanced lcollections:

Code:

 <component name="Items" class="MyEnhancedList">
      <bag name="Items" table="..." ...>
        <key column="..."/>
        <one-to-many class="MyItemClass"/>
      </bag>
 </component>

Items is a property in your collection implementation that contains the items:

Code:

    public abstract class ListBase<T> : IList<T>, IList where T : class
    {
        private IList<T> items;

        protected ListBase()
        {
            items = new List<T>();
        }

        public IList<T> Items
        {
            get { return items; }
            protected set {items = value; }
        }
...
}

The methods necessary for IList can simply be passed to the inner list. Any additional functionality can go in the wrapper class.

rbirkby · **Joined:** Fri Apr 03, 2009 10:36 am **Posts:** 6

Thanks. That's an ingenious idea. I suppose that would break any Linq to NHibernate support, but I'll definitely investigate it.

Fluent NHibernate implies it's possible to specify a custom collection type here:

http://wiki.fluentnhibernate.org/show/S ... ctionTypes

How does this work behind the scenes? What's the equivalent in .hbm files?

wolli · **Posted:** Sat Apr 04, 2009 3:11 am

You can implement your own collections. You have to implemnt IUserCollectionType on your list. But I've never used that before, so I can't help you there. And if you want to use lazy loading, you'll probably have a lot of work.