Question

I got a follow up question to this question.

I use Silverlight and WCF, where lazyloading isn’t an option. How can i ignore a HasMany relation programmatically in some cases improve performance? (I just want the Foo’s without the related Bars).

Answer 1

Basically, what you’re trying to do is not possible, be it NHibernate or Fluent. You can’t have mapping saying “sometimes load, sometimes not”. Setting Not.LazyLoad() is pretty much show stopper – NHibernate will load collection always, entirely.

Those kind of optimization (sometimes load, sometimes not) are better suited to be handled at DAO part of your model. For example, you could have your FooDao class looking like this:

public class FooDao
{
    public IList<Foo> GetFoosEagerly()
    {
        // load all Foos first; then all Bars for every Foos
        var foos = session.QueryOver<Foo>().List();
        foreach (var foo in foos)
        {
            NHibernateUtil.Initialize(foo.Bars);
        }

        return foos;
    }

    public IList<Foo> GetFooPerformanceCritical()
    {
        return session.QueryOver<Foo>().List();
    }
}

With standard mapping (as in, not using Not.LazyLoad()), first method will still return Foos with Bars collection fully set (we just need to tell NHibernate to load them now, before we return). However, second one tho will return Foo objects only. No single Bar will be loaded. Instead, NHibernate will generate proxy object in place of Bars collection for every Foo.

Your WCF service can use such DAO object internally. Naturally, you can have similar methods to load single Foo.

Conclusion is simple; mappings alone won’t help you with your problem. You need to do some extra coding work, but it definitely is possible.