NHibernate. get singleOrDefault

Question

I have the following method. This returns a single unqiue order. However i just want the first result. What is the best way to achieve this. Of course i could return a List and then get the first result from that.

ie .List<Order>().SingleOrDefault();

Surely there is away through the criteria api to acheive this?

    Model.Order order = _session
            .CreateCriteria(typeof(Model.Order))
            .Add(Restrictions.Eq("UserName", user.UserName))
            .Add(Restrictions.Eq("CompanyId", companyId))
            .Add(Restrictions.Eq("OrderStatus", OrderStatusHelper.OrderOpen()))
            .AddOrder(sortOrder)
            .UniqueResult<Model.Order>(); // results not always unique

Answer 1

    IList<Model.Order> order = _session
        .CreateCriteria(typeof(Model.Order))
        .Add(Restrictions.Eq("UserName", user.UserName))
        .Add(Restrictions.Eq("CompanyId", companyId))
        .Add(Restrictions.Eq("OrderStatus", OrderStatusHelper.OrderOpen()))
        .AddOrder(sortOrder)
        .SetMaxResults(1)
        .List<Model.Order>(); // results not always unique

        if(order.Count == 1)
        {
             return order[0];
        }
        else
        {
             return default(Model.Order)
        }

Something like this.

Answer 2

It's slightly less complicated than Saint Gerbil proposed:

Model.Order order = _session
        .CreateCriteria<Model.Order>()
        .Add(Restrictions.Eq("UserName", user.UserName))
        .Add(Restrictions.Eq("CompanyId", companyId))
        .Add(Restrictions.Eq("OrderStatus", OrderStatusHelper.OrderOpen()))
        .AddOrder(sortOrder)
        .SetMaxResults(1)
        .UniqueResult<Model.Order>();

This will do a query using the DB syntax for retrieving only one record.

If there are no records matching the criteria, UniqueResult returns null.

You could also use NHibernate Linq (either the 2.x contrib provider, or the one integrated in NH 3.x). In that case, you should use FirstOrDefault instead of SingleOrDefault to achieve the result you want.