ASP.NET MVC + Entity Framework with Concurrency check

Question

I am trying to implement a application following the sample in this page: http://www.asp.net/entity-framework/tutorials/handling-concurrency-with-the-entity-framework-in-an-asp-

Answer 1

It doesn't work this way. Once you load entity by Find you cannot change its timestamp directly. The reason is that timestamp is computed column. EF holds internally original and current values for each loaded entity. If you change the value in the loaded entity, only current value is changed and during update EF compares the original value with the current value to know which columns must be updated. But in case of computed columns EF don't do that and because of that your changed value will never be used.

There are two solutions. The first is not loading the entity from database:

public ActionResult Edit(int id, FormCollection collection) 
{
     // You must create purchase order without loading it, you can use model binder
     var purchaseOrder = CreatePurchaseOrder(id, collection);
     db.Entry(purchaseOrder).State = EntityState.Modified;
     db.SaveChanges();
}

The second solution is small hack described in linked question for ObjectContext API. If you need this for DbContext API you can try something like:

public ActionResult Edit(int id, FormCollection collection) 
{
     var purchaseOrder = db.PurchaseOrders.Find(id);
     purchaseOrder.Timestamp = GetTimestamp(collection);
     // Overwrite original values with new timestamp
     context.Entry(purchaseOrder).OriginalValues.SetValues(purchaseOrder);
     UpdateModel(purchaseOrder, "PurchaseOrder", collection);
     db.SaveChanges();
}