I want to update an Entity using values from the unique constraint. I know those values in code when I want to update, but do not have the the primary key.

I could of course do:

MyEntity entity = new MyEntity();
entity.FetchUsingUCBlah(12,12,115);
entity.SomeField=12;
entity.Save();

However, I dont want to have to fetch it, just to update a field when I have the values for the UC. This may already work, but the documentation does not mention it and this thread I found seems to indicate it does not.

http://www.llblgen.com/tinyforum/Messages.aspx?ThreadID=4708&HighLight=1

Any help here?

If your sure of the unique constraint then you can directly update rows in the database using a filter. So if your filter defines the Unique Constraint then you would only update that row with the new value. Here's an example from the manual.

// C#
OrderEntity newValues = new OrderEntity();
newValues.EmployeeID = 5;
OrderCollection updater = new OrderCollection();
updated.UpdateMulti(newValues, (OrderFields.EmployeeID == 2));

Ok. I will put that in.

Question - Shouldn't we be able to save with UC values just like with PKey values (in theory)?

SomeEntity entity = new SomeEntity();
entity.PartOfUC1 = 1;
entity.PartOfUC2 = 2;
entity.IsNew = false;
entity.SomeValueToChange = 55;
entity.Save();

Seems like that would be a good feature - I would not have to know which way to code it, just fill out any UC values or PKey values and it work.

UC's are defined in the generated code, not in the meta-data of the entity. This means that saving using a UC requires you to specify an update restriction filter.