Using database generated GUID and datetime with EF4

I have a simple table with an ID (a uniqueidentifier), a datetime, and a value.

I'd like to use getdate() on the database for the record insertion time and newid() for the id. How do I configure entity framework to do this? When I try to assign the id on the DB I get:

Violation of PRIMARY KEY constraint 'PK_Random'. Cannot insert duplicate key in object 'dbo.Random'. The duplicate key value is (00000000-0000-0000-0000-000000000000).