decrement_counters_before_last_save

# File activerecord/lib/active_record/associations/belongs_to_association.rb, line 61
      def decrement_counters_before_last_save
        if reflection.polymorphic?
          model_type_was = owner.attribute_before_last_save(reflection.foreign_type)
          model_was = owner.class.polymorphic_class_for(model_type_was) if model_type_was
        else
          model_was = klass
        end

        foreign_key_was = owner.attribute_before_last_save(reflection.foreign_key)

        if foreign_key_was && model_was < ActiveRecord::Base
          update_counters_via_scope(model_was, foreign_key_was, -1)
        end
      end