Details View and Drop Down List

Question

I have a details view and in the details view I have two template fields together with other fields. Those template fields are dropdown lists. The first dropdown list displays Departments and the second one displays Products. Both of them are populated from the database. I want to display only those products in the Products (second dropdown list) which belong to the department (first dropdown list) which is selected by the user. I am trying to set the select parameter, but details view does not allow me to do it. Can you please help me?