code: function(instance) {
      var args = _.rest(arguments);
      var objects = _.flatten(args);
      this.beforeAddingObjects(instance, objects);
      this.associateObjects(instance, objects);
      return Actionable.create(instance.save.bind(instance));
    }
docs: The add objects method for this relation.
  
  This method invalidates the {@link HasMany#objectsQuery} cache and adds
  the related objects to the {@link HasMany#collection} (if loaded).
  
  It is accessible on an individual model via `add<Singular>` and
  `add<Plural>`. For instance a user that has many articles would cause this
  method to get triggered via `user.addArticle` or `user.addArticles`.
  
  The naming conventions are set forth in {@link HasMany#overrides}.
  
  Mixins can override {@link HasMany#addObjects} to change the way related
  objects are added. This is the default implementation.
  
  @method
  @protected
  @param {Model} instance The model instance on which to operate.
  @param {...Object} [args] The arguments to the method.
  @return {Actionable} A thenable object, use of which will trigger the
  instance to be saved.
  @see {@link BaseRelation#methods}