When you set Auto Generated Value to true, LINQ leaves it up to the database to set the default value. So while the instance of your object is new and not committed, the PK value is Guid.Empty. When you SubmitChanges() the database creates a default value and your LINQ object will have the ID from there out. However, you might want the option to set the default value from code as well. In that case, with Auto Generated Value turned on, if you set the ID from code, the database will still create a new default value when you SubmitChanges. This is obviously not a good scenario because the database won't have the ID you intended to set. So I found a way around this... Instead of setting Auto Generated Value to true, add the following partial method to your class.

partial void OnCreated() { Id = Guid.NewGuid(); }

That's it! This will force LINQ to create a default value right when an instance of the object is created. You will have access to the right ID value from your code before and after committing it to the database!

If you aren't very familiar with partial methods yet this is a good article. blogs.msdn.com/.../in-case-you-haven-t-heard.aspx