Apologies, my previous message was in error. Without more of your
source, it's hard to tell what's going wrong, though.
Also, this pattern:
db.GqlQuery("SELECT * FROM Checkpoint WHERE checkpoint_id = %s" %
(bus.checkpoint_id))
is extremely dangerous. You should never, ever do string substitution
in a GQL (or SQL!) query. GQL directly supports parameterized queries,
so instead you can equivalently (and far more safely) do:
db.GqlQuery("SELECT * FROM Checkpoint WHERE checkpoint_id = :1",
bus.checkpoint_id)
-Nick Johnson
On Apr 21, 1:07 pm, "Nick Johnson (Google)" <[email protected]>
wrote:
> Hi Dmitry,
>
> The issue here isn't with the query, but with your code that's calling
> it. Python is throwing an exception because your variable 'bus' that
> you're trying to fetch checkpoint_id on is set to None, not because
> the result of the query is None. The query code never gets run.
>
> -Nick Johnson
>
> On Apr 21, 12:56 pm, Dmitry Kachaev <[email protected]> wrote:
>
> > I use following construction to lookup records from datastore:
>
> > point_old=models.Checkpoint.all().filter("checkpoint_id
> > =", bus.checkpoint_id).get()
>
> > It works fine in most scenarios, but sometime I'm getting error like
> > this:
>
> > 'NoneType' object has no attribute 'checkpoint_id'
> > Traceback (most recent call last):
> > File "/base/python_lib/versions/1/google/appengine/ext/webapp/
> > __init__.py", line 501, in __call__
> > handler.get(*groups)
> > File "/base/data/home/apps/xxx/1.332943763447248076/tasks/
> > busupdate.py", line 22, in get
> > self.update(bus)
> > File "/base/data/home/apps/xxx/1.332943763447248076/tasks/
> > busupdate.py", line 45, in update
> > self.check_points(bus)
> > File "/base/data/home/apps/xxx/1.332943763447248076/tasks/
> > busupdate.py", line 86, in check_points
> > logging.debug("found old checkpoint: %s" %
> > (point_old.checkpoint_id))
> > AttributeError: 'NoneType' object has no attribute 'checkpoint_id'
>
> > Basically, get() returns None, but record I looked up is definitely in
> > datastore.
>
> > I figured out and replaced this look up call with equivalent GQL call:
>
> > point_old = db.GqlQuery("SELECT * FROM Checkpoint WHERE
> > checkpoint_id = %s" % (bus.checkpoint_id)).get()
> > #point_old=models.Checkpoint.all().filter("checkpoint_id
> > =", bus.checkpoint_id).get()
>
> > What is wrong? Those constructs should behave the same way, but they
> > don't. Commented one is not returning a record, when GQL is returning
> > single record, just fine.
>
> > Thanks,
> > Dmitry
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