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.