nhibernate Restrictions.Eq和null

Question

Advertisements advertisements = NHibernateSession.CreateCriteria(typeof(Advertisements))
                    .Add(Restrictions.Eq(AdvertisementsProperties.Price.ToString(), price))
                    .Add(Restrictions.Eq(AdvertisementsProperties.HollidayDuration.ToString(), hollidayDuration))
                    .Add(Restrictions.Eq(AdvertisementsProperties.Name.ToString(), name))
                    .Add(Restrictions.Eq(AdvertisementsProperties.Description.ToString(), description))
                    //.Add(Restrictions.Eq(AdvertisementsProperties.DepartureDate.ToString(), departureDate))
                    .Add(Restrictions.Eq(AdvertisementsProperties.City.ToString(), city))
                    .Add(Restrictions.Eq(AdvertisementsProperties.Area.ToString(), area))
                    .Add(Restrictions.Eq(AdvertisementsProperties.Country.ToString(), country))
                    .Add(Restrictions.Eq(AdvertisementsProperties.Agency.ToString(), agency))
                    .UniqueResult<Advertisements>();

但是城市，地区或国家/地区可以为空。如何将DB中的null与nhibernate进行比较？

Answer 1

public AbstractCriterion EqOrNull(string property, object value) {
    if (value == null)
        return Restrictions.IsNull(property);
    return Restrictions.Eq(property, value);
}

E.g：

session.CreateCriteria<Advertisements>()
       .Add(EqOrNull(AdvertisementsProperties.City.ToString(), city));

另见HHH-2951

Answer 2

session.CreateCriteria<Advertisements>()
       .Add(Expression.Or(
                 Expression.Eq("AdvName", "Cool Advertisement"),
                 Expression.IsNull("AdvName"))
        ).List<Advertisements>();