thanks - I got bit by those __init__ nuances over the weekend. I ended
up passing an optional flag to the __init__ to say "this is really a
new() vs a datastore reconstitution". I del the optional flag from
kwargs before calling the super __init__. In the datastore
reconstitution case, I do nothing but call the super __init__.
Does that cover the __init__ gotchas, or am I digging my own grave by
not converting to a distinct create function?
On Mon, Aug 24, 2009 at 3:56 AM, Nick Johnson
(Google)<nick.john...@google.com> wrote:
> Hi Jeff,
>
> On Sat, Aug 22, 2009 at 7:24 PM, Jeff Enderwick <jeff.enderw...@gmail.com>
> wrote:
>>
>> Currently, one must put() in order to have obj.key() be valid. In some
>> flows, I find my self having to put() object twice for this reason.
>>
>> If I make a synthetic key, it appears that I can avoid this:
>>
>> class Joker(db.Model):
>> unused = db.StringProperty()
>> def __init__(self):
>> m = hashlib.sha1()
>> m.update(str(time.time()))
>> name = base64.b64encode(m.digest())
>> logging.debug("name="+name)
>> db.Model.__init__(self, key_name=name)
>>
>> 1) GOOG folks - are there any performance downsides to taking this
>> approach?
>
> Not really, no.
>
>>
>> 2) If no, are there any other environmental factors that might be
>> fodder for the hash (user, etc)?
>
> I would recommend using uuid.uuid4().hex instead of a straight SHA1 sum.
> UUIDs are guaranteed to be unique.
> I would also recommend defining a class method called something like
> 'create' that generates the key name and calls __init__. There are
> subtle-use cases around __init__ and reconstructing entities from the
> datastore, and it's difficult to get right - much more straightforward to
> define a class method to construct new entities.
> -Nick Johnson
>>
>>
>> Thanks,
>> Jeff
>>
>>
>
>
>
> --
> Nick Johnson, Developer Programs Engineer, App Engine
>
> >
>
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