gistfile1.rb

  after_save :save_log_entries

  def save_log_entries
    return unless @log_entries
    @log_entries.each { |e| e.save }
    @log_entries = []
  end

#in change_subscription method.....

    @log_entries ||= []
    if new_account_level != self.account_level
      @log_entries << SubscriptionLog.new(
        subscription_id: self.id,
        type_id: Subscription::CHANGE_ACCOUNT_TYPE_CODE,
        account_level_before: self.account_level,
        account_level_after: new_account_level,
        billing_type_before: self.billing_type,
        billing_type_after: new_billing_type
      )
    end
    if new_billing_type != self.billing_type
      @log_entries << SubscriptionLog.new(
        subscription_id: self.id,
        type_id: Subscription::CHANGE_BILLING_TYPE_CODE,
        account_level_before: self.account_level,
        account_level_after: new_account_level,
        billing_type_before: self.billing_type,
        billing_type_after: new_billing_type
      )
    end