Comments on: When is a record really updated_at in Ruby on Rails (and the under-overlooked Observer class)?

By: Rob Cameron

Rob Cameron — Mon, 20 Jul 2009 19:40:42 +0000

Rails 2.3.3, released today, finally has built-in support for a child model to automatically update its parent’s updated_at field when the child is saved! In the association that has the belongs_to association just add:

# /app/models/comment.rb
belongs_to :post, :touch => true

Now when you create/edit/delete a comment then the post it belongs to gets updated_at set to Time.now. You can also name another field if you want:

# /app/models/comment.rb
belongs_to :post, :touch => :last_comment_at

Instead of Post.updated_at being set to now, Post.last_comment_at is set instead.

By: ctagg

ctagg — Thu, 26 Mar 2009 22:53:52 +0000

David
Good point. Thanks for the comment

By: David Reese

David Reese — Thu, 26 Mar 2009 19:15:10 +0000

Hi,

Helpful post, thanks.

One update — now, ActiveRecord records that are not changed do not have their updated_at timestamp updated when saved — record.save does nothing to an unchanged record. You have to do a record.update_attribute(:updated_at, Time.now), as you include above.

By: sazwqa

sazwqa — Tue, 16 Dec 2008 04:48:08 +0000

nice writeup, useful !