Hello Kwon OhJong,
Before you can perform any operations on persistent objects, you should start a transaction. This is done with the ITransaction.Begin() method. Any modifications made to an object after beginning the transaction can be stored in the database by calling ITransaction.Commit(). Performing an update operation inside a foreach loop would look like this:
List<UserStudy> = scope.Extent<UserStudy>().Where(c => c.UserId == id).ToList();
You can find additional information about all write operations in this article
Hope that helps.
the Telerik team