当属性等于Max with NHibernate时选择对象

Question

We have a query that selects rows depending on the value of another, ie. the max. I don't think that really makes much sense, so here is the query:

var deatched = DetachedCriteria.For<Enquiry>("e2")
   .SetProjection(Projections.Alias(Projections.Max("Property"), "maxProperty"))
   .Add(Restrictions.EqProperty("e2.EnquiryCode", "e.EnquiryCode"));

session.CreateCriteria(typeof(Enquiry), "e")
   .Add(Subqueries.PropertyEq("Property", deatched))
   .AddOrder(Order.Asc("EnquiryCode"));

My question is, is this the best way? Can anyone suggest a better way?

Answer 1

You should be able to do this with projection:

session.CreateCriteria(typeof(Customer))
  .SetProjection( Projections.Max("Id") )
  .UniqueResult();

As described Nhibernate Criteria: 'select max(id)...'

Answer 2

对于聚合，最好使用SQL而不是HQL。使用Nhibernate仅用于主要实体及其关系（非常易于维护的设计）。存储过程是这些聚合和函数的更好位置，因为它们依赖于数据而不依赖于对象

Answer 3

I think this must work:

(from e in NHibernateSession().Query<Enquiry>()
    where e.Property == (
    (
        from e2 NHibernateSession().Query<Enquiry>()
        where e2.EnqueryCode == e.EnquiryCode
        select e2.Property).Max()
    )
    select e
).ToList<Enquiry>()