class methods from module where active rec is involved

I have a module as shown below and when I extend an active record to
use it, I can not access the
primary_key method. In a simple test program using a similar approach
where active record is not involved, access to the class methods seems
to work ok. What can I do to make this work or so that I can access
the class methods ?

oops, I needed to do

self.primary_key = 'something'

oops, I needed to do

self.primary_key = 'something'