def handle_shorting(self, url, given_sid):
sid = given_sid or self.shortifier(url)
with self.uow.start() as tx:
surl = tx.short_urls.get(sid)
if surl:
# collision happened
raise SidCollisionException("Collision")
surl = ShortUrl(sid, url)
surl.user = self.user
tx.short_urls.add(surl)
tx.commit()
return sid
