title: NHibernate bulk loading child objects for multiple parents
body: <p>Let's say we have a Category table and Product table. And each Product references Category. So each Category has many Products.
  I want to load many Categories without Products(to decrease DB access time) then check what Categories we actually need and define a much less subset of Categories. 
  After this I need to load all Products for selected Categories and attach them to Categories with a single DB query.
  I can load Products separately but in that case they will not be attached to Categories.</p>