Is there one Oracle DB or are there several and which one needs to be determined based on the user or some other criteria? The article you link to talks about the latter.
It it's just one DB and you have one or more tables to be 'statically' connected to that DB , then see Peak Obsession and look for the section "Connection to multiple databases in different models"
You probably want to call establish_connection with the right connection parameters for the table(s) to be connected to the oracle DB in your config/environment.rb file in a config.after_initialize block. If you've got several tables you can make an abstract AR class for those models to subclass, and establish the connection for the abstract class which will take care of the subclass.
I'm working on a project right now which does something similar. One thing I've found is that most of the testing infrastructure of rails doesn't really handle tables with their own connections very well, what I've done is to put analogs of those tables directly in the main test environment database. I wrote the migrations for the 'external' tables so that they only actually create the tables if ENV['RAILS_ENV'] is 'test'
