Rails 4: .save not updating update_at for existing records?

Question

I always thought that .savethey .save!would update the column of updated_atexisting records. Is that not so? If so, do I need to create a before_save filter to update it every time I save?

Today is June 18th:

    Loading development environment (Rails 4.1.1)
    irb(main):001:0>  o = Order.last
      Order Load (0.4ms)  SELECT  `orders`.* FROM `orders`   ORDER BY `orders`.`id` DESC LIMIT 1
    => #<Order id: 24, user_id: 1, order_date: nil, total_cents: 0, total_currency: "USD", shipping_cents: 0, shipping_currency: "USD", tax_cents: 0, tax_currency: "USD", subtotal_cents: 0, subtotal_currency: "USD", created_at: "2014-06-13 21:24:38", updated_at: "2014-06-13 21:24:38", status: "Incomplete", coupon_id: nil>
    irb(main):002:0> o.save!
       (0.4ms)  BEGIN
       (0.3ms)  COMMIT
    => true
    irb(main):003:0> o.updated_at
    => Fri, 13 Jun 2014 21:24:38 UTC +00:00
    irb(main):004:0> o.reload
      Order Load (0.7ms)  SELECT  `orders`.* FROM `orders`  WHERE `orders`.`id` = 24 LIMIT 1
    => #<Order id: 24, user_id: 1, order_date: nil, total_cents: 0, total_currency: "USD", shipping_cents: 0, shipping_currency: "USD", tax_cents: 0, tax_currency: "USD", subtotal_cents: 0, subtotal_currency: "USD", created_at: "2014-06-13 21:24:38", updated_at: "2014-06-13 21:24:38", status: "Incomplete", coupon_id: nil>
    irb(main):005:0> o.updated_at
    => Fri, 13 Jun 2014 21:24:38 UTC +00:00

I care about this because I wrap the function internals with ActiveRecord::Base.transaction, so I want to check that they are not updated when something goes wrong:

Rspec test (which passes all the time when it should not, because updated_at does not change regardless of success or failure):

  it "rollsback the transaction" do
    ...
    order.stub(:save!).and_raise(StandardError)
    expect { payment_info.save }.not_to change { [billing_address.updated_at, 
                                                  shipping_address.updated_at,
                                                  order.user.updated_at,
                                                  order.updated_at] }
  end

And my method:

def process_billing_info!
  ActiveRecord::Base.transaction do
    billing_address.save!
    shipping_address.save!
    user.save!
    order.update_all_fees!
  end
rescue Exception => e
  false
end

Answer 1

, UPDATE SQL-, . Rails . , .save , .

.touch, updated_at :

1.9.3p489 :005 > Intervention.first.touch
  Intervention Load (12.9ms)  SELECT "interventions".* FROM "interventions" LIMIT 1
  SQL (20.5ms)  UPDATE "interventions" SET "updated_at" = '2014-06-18 16:34:03.924648' WHERE "interventions"."id" = 1
 => true 

UPDATE SQL.

Answer 2

@MrYoshiji, .touch:

if o.save!
  o.touch unless o.changed?
end