Distinguishing "update or create context" from within after_

Of course, I like the callbacks in active record. However, it seems
that it would be valuable to be able to distinguish whether an
after_save is being invoked as part of a create as opposed to part of
an update scenario.

Is there a best practice for doing this? I assume I can set a flag int
he create or update methods and check in the after_save, but not sure
if this is best practice.

You mean like using the after_create and after_update callbacks instead?