public class GeneratingUnit : DomainObject<int>
    {
        private string name;
        private string fullName;
        private Counterparty counterparty;
        private decimal productionCapacity;
        private IList<GeneratingUnitProduction> production =
                         new List<GeneratingUnitProduction>();
...
}

public class GeneratingUnitProduction : DomainObject<int>
    {
        private GeneratingUnit generatingUnit;
        private DateTime flowDate;
   ...
}

SELECT *
  FROM Generating_Unit
where generating_unit_id NOT IN
       (
        SELECT generating_unit_id
          FROM generating_unit_production
         WHERE Flow_Date = :flowDate
       )

DetachedCriteria subQuery =
                DetachedCriteria.For(typeof (GeneratingUnit)).SetProjection(Projections.Id()).CreateCriteria(
                    "Production").Add(Restrictions.Eq("FlowDate", flowDate));
            return
                new List<GeneratingUnit>(
                    Session.CreateCriteria(typeof (GeneratingUnit))
                    .Add(Subqueries.PropertyNotIn("Id", subQuery))
                    .List<GeneratingUnit>());

DetachedCriteria subQuery =
                DetachedCriteria.For(typeof (GeneratingUnit)).SetProjection(Projections.Id()).CreateCriteria(
                    "Production").Add(Restrictions.Eq("FlowDate", flowDate));
            return
                new List<GeneratingUnit>(
                    Session.CreateCriteria(typeof (GeneratingUnit))
                    .Add(Subqueries.PropertyNotIn("Id", subQuery))
                    .List<GeneratingUnit>());

DetachedCriteria subQuery =
    DetachedCriteria.For(typeof (GeneratingUnit))
          .SetProjection(Projections.Id())
          .CreateCriteria("Production")
              .Add(Restrictions.Eq("FlowDate", flowDate));

return new List<GeneratingUnit>(
    Session.CreateCriteria(typeof (GeneratingUnit))
          .Add(Subqueries.PropertyNotIn("Id", subQuery))
         .List<GeneratingUnit>());