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A couple of items with NH Linq to keep in mind:
This Linq release support just about anything that you can do with the criteria API. We do not support group joins or subqueries in select clauses, since they arenâ€™t supported by the criteria API. NHibernateâ€™s Linq support has been tested (in production!) for the last couple of years, and most people find it more than sufficient for their needs.