Get Nhibernate entity and complete it from a web service.

Question

Hi every one. let's say that i have an order system. each "Order" references a "Customer" Object. when i fill the orders list in Data Access Layer, the customer object should be brought from a Customer Web Service "WCF". so i didn't map the Customer property in the Order mapping class,

        Id(o => o.OrderID).GeneratedBy.Identity();
        //References(o => o.Customer).Not.Nullable().Column("CustomerID");
        HasMany(o => o.Details).KeyColumn("OrderID").Cascade.AllDeleteOrphan();
        Map(c => c.CustomerID).Not.Nullable();

and asked the nhibernate session to get me the orders list. and tried to loop on every order in the list to fill it's customer property, doe's any body have a good idea for this ????

 IList<Order> lst = Session.CreateCriteria<Order>().List<Order>();
 foreach (Order order in lst)
                order.Customer = serviceProxy.GetCustomerByID(order.CustomerID);

Answer 1

So you're saying that you hit your WCF, for Order list of 50, 50 times. Not so good.

You should do this:

   var customers = serviceProxy.GetCustomersForIDs(lst.Select(x => x.CustomerID).Distinct()); //one hit to WCF

   foreach(var order in lst)
        order.Customer = customers.Single(x => x.ID == order.CustomerID);

That is for performance vise.

The other thing that you can do and be fancy (and not so performace oriented, but exactly the same performace as your sample):

modify property Customer as this:

       private customer;
       public virtual Customer
       {
            get
            {
                 if(customer == null)
                     customer = serviceProxy.GetCustomerByID(this.CustomerID);
                 return customer;
            }
        }

Where your order should have a reference to serviceProxy.

Answer 2

If you really want to do this transparently, try implementing a custom tuplizer (and associated things). Take a look at this article, it implements a remote lazy loader for Java Hibernate, however the general concepts apply equally to NHibernate since it has the same overall design (tuplizers, lazy initializers, proxy factory, etc).