Rails Single Table Inheritance using Foreign Key (ID)

Question

Hi,

I have to model an association structure and the association is divided into divisions/subdivisions/sections etc. So I've created a simple Entity-Attribute Model:

I'd like to use rail's single-table-inheritance but it seems like this works only if the type column is a string. My question is how to achieve this with my approach? Since I'm using a foreign key as "type" I'd have to query the "type name" first. Has anybody done this before?