I have:
class Ruser < ActiveRecord::Base
has_many :deliveries
has_many :bags, :through => :deliveries
class Bag < ActiveRecord::Base
has_many :deliveries
has_many :rusers, :through => :deliveries
class Delivery < ActiveRecord::Base
belongs_to :ruser
belongs_to :bag
Delivery has an extra attribute :delivered_at of type date.
I have Ruser and Bag already populated.
I want to assign bags to rusers simultaneously setting delivered_at.
Doing user.bags << bags doesn't allow to set delivered_at.
