i use this code to have snapshots
$user->username='ali';
$user->status='N';
$user->save();
$user->username='ali2';
var_dump($user->getChangedFields());
var_dump($user->hasChanged('username'));
var_dump($user->hasChanged('status'));
but i have this error : The record doesn't have a valid data snapshot' in phalcon/mvc/model.zep on line 3628