Greetings,

I am writing a WPF application and want to use NHibernate. To avoid writing a UI layer over my domain model (at first, at least), and to make data binding work well with my domain objects, I would like to have all of my collections implement INotifyCollectionChanged and my domain objects implement INotifyPropertyChanged. Doing this will make the data binding "just work".

I was impressed with the level of control NHibernate gives you for domain objects, basically giving you unlimited freedom in inheriting and implementing whatever you desire.

Unfortunately, I don't see the same flexibility with what collections NHibernate uses. There is no way (that I can see) to make the collections implement any interface because the collections are using proxies to update themselves.

So, my question is, are there any plans to include these interfaces optionally in the collections? If not, do I have any options for getting my collections to implement these interfaces on my own other than changing the NHibernate codebase?

Thanks,
Michael Hedgpeth

I've done more investigation in the codebase and see that the collections are hard-coded into the system.

What would be really nice is if I could provide my own collections that implemented my own interfaces that subclassed the Persistent collections NHibernate uses. It would use a form of configurable dependency injection.

I take it that kind of thing hasn't been considered yet. I supposed I'll update the source code of NHibernate on my machine to suit my needs and move on.

Thanks,
Michael Hedgpeth

Have you seen IUserCollectionType in 1.2.0?

I've worked out a solution for this issue. I developed some collection classes which implement NHibernate's IUserCollectionType and WPF's INotifyCollectionChanged interface that will trigger UI updates when their contents change. Check out my blog article for more info and to download my demo project:

http://analog-man.blogspot.com/2007/01/bridge-gap-between-your-nhibernate.html

I also have a question regarding this topic.

I have used gdereese's blog article to implement a custom collection class implementing "INotifyCollectionChanged". Was wondering how this works when making a query against a particular persistent class.

For example, IList<Book> = _session.CreateCriteria(typeof(Book)).List<Book>(); How could I get this to return an IObservableList<Book> subclass?

Thanks in advance for any comments.

you cannot change the type of collection that a criteria query will return. Your only alternative is to poulate an IObservableList<Book> with an IList<Book>. Custom collection types have nothing to do with results returned from the query API's.

We handled this by using field mapping rather than property mapping (field.camelcase-underscore), with the field that NHibernate sees feeding a private property with a different name. Then the public property whose name does match the field is of our collection type, which uses the composition design pattern to forward to the underlying collection.

So, an example looks like this:



Then OurListType can provide whatever it wants -- we implement IList, IList<T>, IBindingListView, IComparer, etc. Our list type tracks the property name on the item class that references the owner of the list (the "parent"), and automatically sets/clears it when items are added/removed from the list.

Thanks Nels_P_Olsen and jnapier for your replies. Pretty much affirmed what I was thinking. It just seems that if a collection could be mapped to a custom IList<> collection, the same functionality could be added to ICriteria. This would cleanly address binding issues of object lists returned from a query, especially in a WPF application.

After studying gdereese's example, I created an improved solution which includes three types (bag, list, and set) of observable collections. See my blog entry (http://happynomad121.blogspot.com/2007/12/collections-for-wpf-and-nhibernate.html) for further details and to download the solution.