Linq To SQL Attach / Refresh Entity Object

In Linq To Sql, when I update one of my entities, Faculty, I create a new instance of Faculty object, then initialize some properties with user supplied values.

If I attach this new object to the entity set and submit the changes, then the properties I have not set take the default for any data type.

How do I update the new object so that properties that have been set retain their values, and properties that have not been set receive values ​​from the database?

thanks