如何使用POCO和自定义ObjectContext正确更新EF4中的实体？

Question

Using the technique described here I have a simple POCO EF4 model up and running. Saving new and deleting is straightforward (using AddObject() and DeleteObject() respectively). But the only way of updating objects I have found is to retrieve the stored version of the object and manually update its properties with new values from the object being saved. Surely there is a better way?

My ObjectContext is disconnected - in otherwords, I use a new ObjectContext instance for each operation on the model.

Thanks.

Answer 1

Use the stub technique :

public void UpdateOrder(Order o)
{
   var stub = new Order { Id = o.OrderId }; // create stub with EntityKey
   ctx.Orders.Attach(stub); // attach stub to graph
   ctx.ApplyCurrentValues("Orders", o); // override stub with values.
   ctx.SaveChanges();
}

If the entity is already in the graph, you will get an OSM exception (entity with key already exists).

I counteract this by checking if the object exists in the graph first (TryGetObjectStateEntry) and only attaching if it doesn't.