def define_touchable!(association)
      name = association.name
      method_name = define_relation_touch_method(name, association)
      association.inverse_class.tap do |klass|
        klass.after_save method_name
        klass.after_destroy method_name
        klass.after_touch method_name
      end
    end
def define_touchable!(association)
      name = association.name
      method_name = define_relation_touch_method(name, association)
      association.inverse_class.tap do |klass|
        klass.after_save method_name
        klass.after_destroy method_name
        klass.after_touch method_name
      end
    end
Add the association to the touchable associations if the touch option was
 provided.

 @example Add the touchable.
   Model.define_touchable!(assoc)

 @param [ Association ] association The association metadata.

 @return [ Class ] The model class.

 @since 3.0.0