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copied!<p>Although Diego's answer is the accepted method for doing these things in NHibernate, I really don't feel comfortable with that approach. I don't want to have to define explicit contracts for my objects just because I may need to retrieve them in certain ways. Also, I don't always want to serialize them at all. Furthermore, in many cases I know that the best performance will <em>always</em> be a single round-trip to fetch all the data.</p> <p>The solution I ended up using was to implement a function that takes a list of (type safe) expressions on the root object, such as</p> <pre><code>x => x.Child.GrandChild1 x => x.Child.GrandChild2Collection.SubInclude(c => c.GreatGrandChild) </code></pre> <p>Where SubInclude is an extension method for IEnumerable that is used when parsing these expressions.</p> <p>I parse this list of expressions and build, for each subpath of each expression (x, x.Child, x.Child.GrandChild1) an NHibernate criteria query on the root type:</p> <pre><code>var queryOver = session.QueryOver<T>().Where( ...expression to select root objects... ); for every subpath in the current expression: queryOver.RootCriteria.SetFetchMode(subPath, FetchMode.Eager) queryOver.RootCriteria .SetResultTransformer(new DistinctRootEntityResultTransformer()) queryOver.Future() </code></pre> <p>This is repeated for every expression in the list. The last line makes sure that this eager fetch will be included in whatever round-trip happens next. Then I make the actual query on the root object T, and the session automatically performs in that same round-trip all the queries required to fetch each of the paths I've passed in the expressions.</p> <p>The queries are performed separately for each expression path, so there is no cartesian-product problem.</p> <p><strong>Bottom line</strong> is that this is no simple feat. There's a little too much code for me to publish as-is. I prefer EF4.1's Include(expression) API, which does all of this automagically.</p>

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