Jim Fulton wrote:
Right, but to manage the integer ids, we need to be able to turn objects
into keys, since many objects are not valid keys. The key reference
framework provides a way to generate keys from objects. The key reference
adapter for persistent objects has the extremely inconvenient property
that you can't compute a key reference for a persistent object until
it has been added to a database. Key references based on guids wouldn't
have this negative property.
Oh, now I see where GUIDs came in. I would instead propose to make
key references not dependent on OIDs. I would just define a
light-weight way of generating lots of guaranteed-unique IDs.
Something like this, perhaps (this particular implementation requires
Python 2.4):
NUM_ID_BITS = 64
BIGGEST_ID = (2 << (NUM_ID_BITS + 1) - 1)
NUM_TIME_BITS = 48
BIGGEST_TIME = (2 << (NUM_TIME_BITS + 1) - 1)
def getTime():
result = int(time.time()*1000)
assert result <= BIGGEST_TIME
return result
def ids():
last_time = None
while True:
current_time = getTime()
if current_time != last_time:
counter = 0
else:
counter += 1
result = current_time << (NUM_ID_BITS-NUM_TIME_BITS) | counter
assert result <= BIGGEST_ID
yield result
last_time = current_time
getId = ids().next
This give you as many unique IDs you could need, but the resulting ID
would have to be stored on the object, just like the GUID would.
--
Benji York
Sr. Software Engineer
Zope Corporation
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