EF4 Update Entity Without First Getting Entity

How can I update an entity without having to make a call to select it. If I supply the key for the entity, should it not know to update after SaveChanges() is called on the ObjectContext.

I currently do this:

var user = context.Users.Single(u => u.Id == 2);
user.Username = "user.name";
user.Name = "ABC 123";
context.SaveChanges();

That works, but forces a select. Because I know the Id, why can't I do something like this:

var user = new User();
user.Id = 2;
user.Username = "user.name";
user.Name = "ABC 123";
context.UpdateObject(user);
context.SaveChanges();

Thanks in advance.

EDIT: Also, it's important that 开发者_C百科only the affected properties that are changed be updated. Is this possible?

Maybe following code work fine.

var user = new User();
user.Id = 2;
context.Users.Attach(user);

user.Username = "user.name";
user.Name = "ABC 123";

context.SaveChanges();

You can do this in a somewhat artificial way, by adding the entity and changing the EntityState to Modified:

var user = new User();
user.Id = 2;
user.Username = "user.name";
user.Name = "ABC 123";

context.AddToUsers(user);
ObjectStateEntry userEntry = context.ObjectStateManager.GetObjectStateEntry(user);
userEntry.ChangeState(EntityState.Modified);

context.SaveChanges();

In this way you will be telling the ObjectContext to find an entry with Id = 2 and update it rather than adding a new entry to the database.

Didn't you have to select it anyway to get it's data to edit? If you cache it it won't cost you anything getting it again when you save it.