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'