ActiveRecord::HasManyThroughAssociation NotFoundError - Ruby on Rails

I ran into a bit of a problem with a has_many relationship in rails today:

ActiveRecord::HasManyThroughAssociationNotFoundError in FeedbacksController#index
…
Could not find the association :sub_orders in model User

This turned out to be a fairly simple fix, I had forgotten to add a has_many relationship before adding the has_many :through => x relationship. There is a fairly detailed explanation on StackOverflow for anyone who is curious.