Question

Given that

public abstract class AbstractOrder
{
    //some properties...
}

public class AnonymousOrder:AbstractOrder
{
    //some properties...
}


public class PartnerOrder:AbstractOrder
    {
        //some properties...
    }


public AbstractOrder FindOrderByConfirmationNumber(string confirmationNumber)
{
    ICriteria criteria =
        Session.CreateCriteria(typeof(AbstractOrder))
            .SetMaxResults(10)
            .AddOrder(Order.Desc("PurchasedDate"))
            .Add(Restrictions.Eq("ConfirmationNumber", confirmationNumber));
    var l = criteria.List<AbstractOrder>();
    AbstractOrder ao = l[0] as AbstractOrder;
    return ao as AbstractOrder;
}

Can someone please explain why

PartnerOrder order = repo.FindOrderByConfirmationNumber(confirmationNumber)

returns a type of AnonymousOrder and how I get it to return a type of PartnerOrder?

Answer 1

FindOrder is returning a type of AbstractOrder; just look at its declaration. The object it returns may be an instance of AnonymousOrder, but all AnonymousOrder instances are also AbstractOrder instances, because AnonymousOrder inherits from AbstractOrder.

I think your real problem is trying to assign an AnonymousOrder instance to a PartnerOrder reference. This won’t work, since neither type is derived from the other.

This, however, will work:

AnonymousOrder order = (AnonymousOrder)repo.FindOrderByConfirmationNumber(confirmationNumber);

Alternatively, you could test the type of the return value:

AbstractOrder order = repo.FindOrderByConfirmationNumber(confirmationNumber);
PartnerOrder partnerOrder = order as PartnerOrder;
if (partnerOrder != null)
    //...

If you really need a PartnerOrder instance for a confirmationNumber that returns an AnonymousOrder, then you’ll need a method that takes an AnonymousOrder instance and returns a PartnerOrder instance. Or, perhaps, you should rethink your design.