gistfile1.rb

def card_assign card, employee
  active_card = card.card_assignments.all(:conditions=>["active_since < #{DateTime.now} and #{DateTime.now} < active_until"]).first

  if not current_card.nil? then
    active_card.active_until = DateTime.now
  end

  active_card = CardAssignment.new
  active_card.active_since = DateTime.now
  active_card.active_until = DateTime.now + 1 year
  active_card.first_time = true
  employee.card_assignments.add active_card
  card.card_assignments.add active_card
end