Ruby on Rails

belongs_to :resellercategory
has_one :subcategory, :through => :resellercategory
has_one :category, :through => :subcategory

So, there are a lot of resellercategories that are (manually) mapped to my fewer subcategories.

I have a before_save in my products model that sets if the product is complete:

  def check_complete
    self.complete = !image_small.blank? && !subcategory.blank?
    nil
  end

So, if the resellercategory that the product is related to is mapped to a subcategory, the product is marked as "complete". However, at the moment it is only updated when the product is saved, I also want it to be updated when the resellercategory is mapped to a subcategory.

Is there any good way to do this? Should I create an after_save in my resellercategory that iterates through all the products and re-saves all of them to get the field updated?
Any easier/more effective way?

Regards
Linus