For posterity, one such gotcha is a case where Model instances work
fine, but Expando instances can loose their additive attributes coming
back out of the datastore. Switched to factory @staticmethod, and all
is good now...
On Tue, Aug 25, 2009 at 6:32 AM, Nick Johnson
(Google)<nick.john...@google.com> wrote:
> On Mon, Aug 24, 2009 at 6:44 PM, Jeff Enderwick <jeff.enderw...@gmail.com>
> wrote:
>>
>> 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?
>
> I don't know the gotchas well enough to say. I still think a factory
> function is your best bet. :)
> -Nick Johnson
>
>>
>> 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
>> >
>> > >
>> >
>>
>>
>
>
>
> --
> Nick Johnson, Developer Programs Engineer, App Engine
>
> >
>
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