SugarCRM: check updating of object’s property

Sometimes it’s needed to know about updating of specified object’s property. SugarCRM keeps previous values for all object’s properties in the array fetched_row. For example, to realise it’s new object or just updated we should compare ID from that array and current value of object’s property:
if($obj->fetched_row['id'] != $obj->id) {
echo "This's a new object!\n";
} else {
echo "This's an existing object\n";

That approach might be used in the handler of logic hook, for example, to perform some action when desire property is changed.