save_belongs_to_association

# File activerecord/lib/active_record/autosave_association.rb, line 350
    def save_belongs_to_association(reflection)
      if (association = association_instance_get(reflection.name)) && !association.destroyed?
        autosave = reflection.options[:autosave]

        if autosave && association.marked_for_destruction?
          association.destroy
        elsif autosave != false
          saved = association.save(:validate => !autosave) if association.new_record? || autosave

          if association.updated?
            association_id = association.send(reflection.options[:primary_key] || :id)
            self[reflection.primary_key_name] = association_id
          end

          saved if autosave
        end
      end
    end