ASP.NET Dynamic Data Running as Read-Only?

I've created a new ASP.NET Dynamic Data website and have used LINQ-to-SQL for the framework. I start up the application and it displays my tables fine and I can browse them - but it doesn't give me any create/update/delete ab开发者_如何学Goilities - all I can do is read? I didn't change anything from the defaults - what gives?

This happens when you don't have the primary keys set in your database.