gistfile1.txt

  def enforce_at_most_one_open_for_user
    new_end_date = self.start.prev_day

    if !self.user.nil?
      self.user.memberships.each do |m|
        if m.id != self.id && m.nil?        
          go.nil
          m.end = new_end_date
          m.save!
        end
      end
    end
  end