So you want to use CForm (form builder), but need to preload dropdowns in a form? It's simpler than it seems.
You got your CFormModel, CForm and the actual Form, right?
Let's say you have the typical State -> City dependent dropdowns, so you would want to load the from with the State and City selected.
Relational databases do not support inheritance so if we need to represent it, we have to somehow store meta info while keeping performance by minimizing JOINs. One way to solve this problem is using single table inheritance. All fields for the whole class tree are stored in a single table. Class name is stored in the type field of the same table.