Touch an ActiveRecord - timestamps

rubyonrails-talk
1

When I update an ActiveRecord, i would like to "touch" one of the related objects, that the updated record belongs_to, in order to update the timestamps on the parent record, although i don't want to change any of the data in the parent. Whats the accepted way to do this?

2

just calling save on the parent association works in my testing, e.g.   some_child.some_parent.save

3

Jeff Emminger wrote:

just calling save on the parent association works in my testing, e.g.   some_child.some_parent.save

On Nov 13, 10:08�am, David Warburton <rails-mailing-l...@andreas-

That was the first thing i tried :(. I have rails 2.1.1.

4

working for me in 2.1.2

# parent class class Team < ActiveRecord::Base   has_many :games end

# child class class Game < ActiveRecord::Base   belongs_to :team end

# unit test require 'test_helper' class GameTest < ActiveSupport::TestCase

  def test_updates_parent_timestamps     team = Team.create(:name => 'Team 1')     game = Game.create     team.games << game

    team.save

    assert team.valid?     assert game.valid?

    old_date = team.updated_at     game.team.save

    assert_not_equal old_date, team.reload.updated_at   end

end

5

working for me in 2.1.2

# parent class class Team < ActiveRecord::Base has_many :games end

# child class class Game < ActiveRecord::Base belongs_to :team end

# unit test require 'test_helper' class GameTest < ActiveSupport::TestCase

def test_updates_parent_timestamps team = Team.create(:name => 'Team 1') game = Game.create team.games << game

team\.save

assert team\.valid?
assert game\.valid?

old\_date = team\.updated\_at
game\.team\.save

assert\_not\_equal old\_date, team\.reload\.updated\_at

end

I expect that passes only because old_date was basically set to Time.now (so has a fractional second component), whereas team.reload.updated_at is fetched from the database, so the fractional portion of the second is lost. In rails 2.1 game.team.save is a no-op because only changed attributes are saved (and here none are changed). You can force a save by modifying any attribute or calling one of the _will_change! methods ie

def touch   updated_at_will_change!   save end

Fred

6

I recommend an observer to do this, and I also recommend using a different column other than updated_at. I use last_modified_at to store the date that any part was changed, and reserve updated_at for tracking when the individual pieces are changed.

Something like this would work, although this is done from memory.

class UpdateObserver < ActiveRecord::Obeserver observe :project, :task, :note, :attachment

def after_save(record) if record.is_a? Project

     p = record
 else
     p = record.project
 end
 p.last_modified_at = Time.now
 p.save!

end

def after_destroy(record) unless record.is_a? Project p = record.project p.last_modified_at = Time.now p.save! end end end