Is their a way to set a relationship field without Globiflow?

I have a campaign app that on creation or update when I set the relationship to another app I update a category field with in the same app to represent the relationship.  

I currently do not have Globiflow so am looking for a solution to do this using either workflow or a calc.

I don't mind if I set the relationship or the category 1st, I just don't want to have to set both manually each time.

I have tried to this in workflow but can't seem to get it working.