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，区域或国家可以为空。我怎样才能将数据库中的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);
}

例如。:

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

另请参阅 HHH-2951