lib/parse/model/associations/relation_collection_proxy.rb
def add(*items)
      items = items.flatten.parse_objects
      return @collection if items.empty?

      notify_will_change!
      additions_will_change!
      removals_will_change!
      # take all the items
      items.each do |item|
        @additions.push item
        @collection.push item
        #cleanup
        @removals.delete item
      end
      @collection
    end
def add(*items)
      items = items.flatten.parse_objects
      return @collection if items.empty?

      notify_will_change!
      additions_will_change!
      removals_will_change!
      # take all the items
      items.each do |item|
        @additions.push item
        @collection.push item
        #cleanup
        @removals.delete item
      end
      @collection
    end
Add Parse::Objects to the relation.
 @overload add(parse_object)
  Add a Parse::Object or Parse::Pointer to this relation.
  @param parse_object [Parse::Object,Parse::Pointer] the object to add
 @overload add(parse_objects)
  Add an array of Parse::Objects or Parse::Pointers to this relation.
  @param parse_objects [Array<Parse::Object,Parse::Pointer>] the array to append.
 @return [Array<Parse::Object>] the collection