Using ActiveRecord, is there a way to get the old values of a record during after_update

Ditto what everyone is saying about transactions.

That said...

ActiveRecord as of Rails 2.1 keeps track of the attribute values of an object. So if you have an attribute total, you will have a total_changed? method and a total_was method that returns the old value.

There's no need to add anything to your model to keep track of this anymore.

Update: Here is the documentation for ActiveModel::Dirty as requested.

Appending "_was" to your attribute will give you the previous value before saving the data.

These methods are called dirty methods methods.

Cheers!

Some other folks are mentioning wrapping all this in a transaction, but I think that's done for you; you just need to trigger the rollback by raising an exception for errors in the after_* callbacks.

See http://api.rubyonrails.org/classes/ActiveRecord/Callbacks.html

The entire callback chain of a save, save!, or destroy call runs within a transaction. That includes after_* hooks. If everything goes fine a COMMIT is executed once the chain has been completed.

If a before_* callback cancels the action a ROLLBACK is issued. You can also trigger a ROLLBACK raising an exception in any of the callbacks, including after_* hooks. Note, however, that in that case the client needs to be aware of it because an ordinary save will raise such exception instead of quietly returning false.