Dealing with POCO in MVVM - wpf

Question

I'm migrating from WinForms world to WPF with MVVM.
My base system works with POCO classes (NHibernate) and we use some DynamicProxy to map this POCO classes into some bindable so the ModelView can expose a proxy of POCO and save a lot of code:
public class OrderViewModel
{
public OrderPOCO Order { get; private set; }
}
public class OrderView
{
public OrderView()
{
DataContext = DynamicProxy(new OrderViewModel(new OrderPOCO()));
}
}
public class OrderPOCO
{
public virtual int Number { get; set; };
public virtual IList<OrderItemPOCO> Items { get; set; };
}
public class OrderItemPOCO
{
public virtual decimal Qty { get; set; }
public virtual decimal Price { get; set; }
public virtual decimal Amount { get; set; }
}
The collection of OrderItemPOCO is binded into a grid. The Amount is a calculated property that depends of some complex rules (I can't put it in the POCO as it's not a simple Amount = Qty * Price).
Sure I can expose in the ViewModel a custom OrderItemViewModel and a collection of OrderItemViewModel but I will need to recode my POCO classes. How I can code this kind of situation in MVVM without recode all my Model?

Answer 1

You are right, you need an OrderItemViewModel. But you don't have to rewrite you model classes, it will remain the same. What you need is something like this:
public class OrderViewModel
{
public OrderViewModel(OrderPOCO order)
{
Order = order;
Items = new ObservableCollection<OrderItemViewModel>(order.Items.Select(o => new OrderItemViewModel(o)).ToArray());
Items.CollectionChanged += OnItemsCollectionChanged;
}
public OrderPOCO Order { get; private set; }
public ObservableCollection<OrderItemViewModel> Items { get; private set; }
private void OnItemsCollectionChanged(object sender, CollectionChangedEventArgs e)
{
// Synchronize this.Items with order.Items
}
}
public class OrderItemViewModel
{
public OrderItemPOCO OrderItem { get; private set; }
}
public class OrderPOCO
{
public virtual int Number { get; set; };
public virtual IList<OrderItemPOCO> Items { get; set; };
}
public class OrderItemPOCO
{
public virtual decimal Qty { get; set; }
public virtual decimal Price { get; set; }
public virtual decimal Amount { get; set; }
}