The common guidance for updates is to keep the original values in view state so that you can recreate the object in its original state, Attach() it and then set the values that the user has modified. This works well for the most part. But at times, a user is allowed to to set only certain values (e.g. Product.UnitsInStock) and is allowed to set them without fear of concurrent change (i.e. optimistic concurrency conflict).
There are two parts to the generated SQL update command:
The code below _simulates_ what you would do with just a few (or one) values available in post-back. Please see this post before using Attach() in a simple 2-tier app. Here, I manually set UpdateCheck to Never for all Product class members one by one in the designer. As a result, the update for UnitsInStock succeeded even though I don’t have the original values.
using (NorthwindDataContext db = new NorthwindDataContext(@"C:\Northwind\Northwnd.mdf"))
db.Log = Console.Out;
// simulate minimal product information available by creating a new one
Product prod = new Product();
// ID is essential and cannot be skipped
prod.ProductID = 8;
// Change just one property
prod.UnitsInStock = 11;
Of course, you must think through very carefully if you want optimistic concurrency check or not. It depends on the semantics of your application.
As an aside, if the designer only provided a single class level property to turn off UpdateCheck for all members, the above solution would be much more palatable. Right now it is a bit tedious when you use the designer.