Question

When a comment on our site gets destroyed, the after_destroy callback is used to update stats:

after_destroy do |p|
  p.topic.update_attribute(:replies, p.replies - 1)
end

I want to be able to do the same thing when a comment gets “soft-deleted”. When a comment is soft-deleted, the comment.visible field is set from 1 to 0.

Is there a way to tell when this happens during the update callbacks? Something like:

after_update do |p|
  if p.visible was changed from 1 to 0, then update stats.
    p.visible.update_attribute(:replies, p.replies - 1)
  end
end

Answer 1

You can do p.visible_changed? to see if it changed. You can also see what it changed from and what it changed to with other methods that ActiveModel::Dirty gives you, which is available by default on all ActiveRecords.