newb question regarding activerecord relationships

Hi Guys,
I've tried searching for this, but haven't come up with the answers.
Sorry, this is a basic question, so sorry for the newb-ness.

Ok so I'm putting together a ruby report that uses ActiveRecord. I
will explain some details below:

So I have an Payment object which inherits from ActiveRecord:
Payment
belongs to invoice
id, invoice_id, amt, date, type

Then I have 3 payment types; Initial, Recur, and Refund that inherit
from Payment. The only differences are that each overrides the type
field.

So my question is this the correct way in setting this up... with only
a payments table with a type field?

I essentially want to do this: Initial.find(:all) and it will pull all
payments with type Initial... instead of doing
Payment.find(:all, :conditions...)

Thanks.

Nevermind.. found what I need to search for. STI (Single Table
Inheritance).

Thanks!