Re: Weird inconsistencies for same queryset in different Django instances

2010-05-11 Thread Malcolm Box 
On Tue, May 11, 2010 at 8:27 PM, Daniel Roseman wrote:

> On May 11, 7:08 pm, Malcolm Box  wrote:
> > Hi,
> >
> > I've run into a weird bug that has me scratching my head - I'm seeing
> > inconsistent results from a queryset between various apache processes and
> > the django shell.  I.e. sometimes a GET gives me the right response (as
> it
> > hits a "correct" Apache instance) and other times it gives a wrong
> > response.  Restarting Apache causes problem to go away, but it resurfaces
> > later.
> >
> > I have a Poll class which has a start_time and an end_time, both of which
> > are optional, plus an enabled field.  A poll is considered active if it's
> > enabled, and if it has a start_time then now > start_time, and if it has
> an
> > end_time then now < end_time.
> >
> > What I'm seeing is that sometimes polls with a start_time that is before
> now
> > are not showing up in the responses when I do a series of GETs.  So e.g.
> > first GET - shows poll, second one - doesn't show, third - doesn't,
> fourth -
> > does and so on.
> >
> > From a fresh python shell, the Poll.objects.active() call always gives
> the
> > right results.
> >
> > The code in question is:
> >
> > class PollManager(models.Manager):
> > def active(self):
> > qs = super(PollManager,
> self).get_query_set().filter(enabled=True)
> > q_start = Q(start_time__isnull=True) |
> > Q(start_time__lte=datetime.datetime.now())
> > q_end = Q(end_time__isnull=True) |
> > Q(end_time__gte=datetime.datetime.now())
> > return qs.filter(q_start,q_end)
> >
> > Where the models are is:
> >
> > class Event(models.Model):
> >enabled = models.BooleanField() # automatic default false
> > other fields
> >
> > class Poll(models.Model):
> > event = models.ForeignKey(Event, db_index=True)
> > enabled = models.BooleanField() # automatic default false
> > start_time = models.DateTimeField(blank=True, null=True,
> help_text="Time
> > to enable this poll (optional)")
> > end_time = models.DateTimeField(blank=True, null=True,
> help_text="Time
> > to close this poll (optional)")
> >
> > objects = PollManager()
> >
> > The view logic is basically:
> >
> > def view_polls(request, event_id):
> > filtered_set =  self.queryset._clone()# Queryset is
> > Poll.objects.active().filter(event__enabled = True)
> > filtered_set = filtered_set.filter(event__id=event_id)
> > return render_to_response(template, filtered_set)
> >
> > (this has been elided and adapted - original code is using
> django-rest-api,
> > JSON responder etc.  But the call boils down to this)
> >
> > I'm confused as to what the problem could be - any clues?
> >
> > Cheers,
> >
> > Malcolm
>
> I'd like to see how the queryset is assigned to `self`. My suspicion
> would be that the arguments are being preserved across requests - when
> it's first instantiated, it correctly uses the current time to filter,
> but on subsequent calls it is still using the time as of the first
> request.
>

The queryset is being initialised in the construction of a callable which is
then used for the view.  So yes, it probably is only being initialised once
on server startup.

Thank you!  Still testing the fix, but I think this will fix it.

Cheers,

Malcolm

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Re: Weird inconsistencies for same queryset in different Django instances

2010-05-11 Thread Daniel Roseman 
On May 11, 7:08 pm, Malcolm Box  wrote:
> Hi,
>
> I've run into a weird bug that has me scratching my head - I'm seeing
> inconsistent results from a queryset between various apache processes and
> the django shell.  I.e. sometimes a GET gives me the right response (as it
> hits a "correct" Apache instance) and other times it gives a wrong
> response.  Restarting Apache causes problem to go away, but it resurfaces
> later.
>
> I have a Poll class which has a start_time and an end_time, both of which
> are optional, plus an enabled field.  A poll is considered active if it's
> enabled, and if it has a start_time then now > start_time, and if it has an
> end_time then now < end_time.
>
> What I'm seeing is that sometimes polls with a start_time that is before now
> are not showing up in the responses when I do a series of GETs.  So e.g.
> first GET - shows poll, second one - doesn't show, third - doesn't, fourth -
> does and so on.
>
> From a fresh python shell, the Poll.objects.active() call always gives the
> right results.
>
> The code in question is:
>
> class PollManager(models.Manager):
>     def active(self):
>         qs = super(PollManager, self).get_query_set().filter(enabled=True)
>         q_start = Q(start_time__isnull=True) |
> Q(start_time__lte=datetime.datetime.now())
>         q_end = Q(end_time__isnull=True) |
> Q(end_time__gte=datetime.datetime.now())
>         return qs.filter(q_start,q_end)
>
> Where the models are is:
>
> class Event(models.Model):
>        enabled = models.BooleanField() # automatic default false
>         other fields
>
> class Poll(models.Model):
>     event = models.ForeignKey(Event, db_index=True)
>     enabled = models.BooleanField() # automatic default false
>     start_time = models.DateTimeField(blank=True, null=True, help_text="Time
> to enable this poll (optional)")
>     end_time = models.DateTimeField(blank=True, null=True, help_text="Time
> to close this poll (optional)")
>
>     objects = PollManager()
>
> The view logic is basically:
>
> def view_polls(request, event_id):
>         filtered_set =  self.queryset._clone()    # Queryset is
> Poll.objects.active().filter(event__enabled = True)
>         filtered_set = filtered_set.filter(event__id=event_id)
>         return render_to_response(template, filtered_set)
>
> (this has been elided and adapted - original code is using django-rest-api,
> JSON responder etc.  But the call boils down to this)
>
> I'm confused as to what the problem could be - any clues?
>
> Cheers,
>
> Malcolm

I'd like to see how the queryset is assigned to `self`. My suspicion
would be that the arguments are being preserved across requests - when
it's first instantiated, it correctly uses the current time to filter,
but on subsequent calls it is still using the time as of the first
request.
--
DR.

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Re: Weird inconsistencies for same queryset in different Django instances

2010-05-11 Thread zinckiwi 
Change your "datetime.now()"s in your manager to "datetime.now"s. The
callable version will be called every time, rather than only once at
the start of the process.

Regards
Scott


On May 11, 2:08 pm, Malcolm Box  wrote:
> Hi,
>
> I've run into a weird bug that has me scratching my head - I'm seeing
> inconsistent results from a queryset between various apache processes and
> the django shell.  I.e. sometimes a GET gives me the right response (as it
> hits a "correct" Apache instance) and other times it gives a wrong
> response.  Restarting Apache causes problem to go away, but it resurfaces
> later.
>
> I have a Poll class which has a start_time and an end_time, both of which
> are optional, plus an enabled field.  A poll is considered active if it's
> enabled, and if it has a start_time then now > start_time, and if it has an
> end_time then now < end_time.
>
> What I'm seeing is that sometimes polls with a start_time that is before now
> are not showing up in the responses when I do a series of GETs.  So e.g.
> first GET - shows poll, second one - doesn't show, third - doesn't, fourth -
> does and so on.
>
> From a fresh python shell, the Poll.objects.active() call always gives the
> right results.
>
> The code in question is:
>
> class PollManager(models.Manager):
>     def active(self):
>         qs = super(PollManager, self).get_query_set().filter(enabled=True)
>         q_start = Q(start_time__isnull=True) |
> Q(start_time__lte=datetime.datetime.now())
>         q_end = Q(end_time__isnull=True) |
> Q(end_time__gte=datetime.datetime.now())
>         return qs.filter(q_start,q_end)
>
> Where the models are is:
>
> class Event(models.Model):
>        enabled = models.BooleanField() # automatic default false
>         other fields
>
> class Poll(models.Model):
>     event = models.ForeignKey(Event, db_index=True)
>     enabled = models.BooleanField() # automatic default false
>     start_time = models.DateTimeField(blank=True, null=True, help_text="Time
> to enable this poll (optional)")
>     end_time = models.DateTimeField(blank=True, null=True, help_text="Time
> to close this poll (optional)")
>
>     objects = PollManager()
>
> The view logic is basically:
>
> def view_polls(request, event_id):
>         filtered_set =  self.queryset._clone()    # Queryset is
> Poll.objects.active().filter(event__enabled = True)
>         filtered_set = filtered_set.filter(event__id=event_id)
>         return render_to_response(template, filtered_set)
>
> (this has been elided and adapted - original code is using django-rest-api,
> JSON responder etc.  But the call boils down to this)
>
> I'm confused as to what the problem could be - any clues?
>
> Cheers,
>
> Malcolm
>
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Weird inconsistencies for same queryset in different Django instances

2010-05-11 Thread Malcolm Box 
Hi,

I've run into a weird bug that has me scratching my head - I'm seeing
inconsistent results from a queryset between various apache processes and
the django shell.  I.e. sometimes a GET gives me the right response (as it
hits a "correct" Apache instance) and other times it gives a wrong
response.  Restarting Apache causes problem to go away, but it resurfaces
later.

I have a Poll class which has a start_time and an end_time, both of which
are optional, plus an enabled field.  A poll is considered active if it's
enabled, and if it has a start_time then now > start_time, and if it has an
end_time then now < end_time.

What I'm seeing is that sometimes polls with a start_time that is before now
are not showing up in the responses when I do a series of GETs.  So e.g.
first GET - shows poll, second one - doesn't show, third - doesn't, fourth -
does and so on.

>From a fresh python shell, the Poll.objects.active() call always gives the
right results.

The code in question is:

class PollManager(models.Manager):
def active(self):
qs = super(PollManager, self).get_query_set().filter(enabled=True)
q_start = Q(start_time__isnull=True) |
Q(start_time__lte=datetime.datetime.now())
q_end = Q(end_time__isnull=True) |
Q(end_time__gte=datetime.datetime.now())
return qs.filter(q_start,q_end)


Where the models are is:

class Event(models.Model):
   enabled = models.BooleanField() # automatic default false
    other fields

class Poll(models.Model):
event = models.ForeignKey(Event, db_index=True)
enabled = models.BooleanField() # automatic default false
start_time = models.DateTimeField(blank=True, null=True, help_text="Time
to enable this poll (optional)")
end_time = models.DateTimeField(blank=True, null=True, help_text="Time
to close this poll (optional)")

objects = PollManager()


The view logic is basically:

def view_polls(request, event_id):
filtered_set =  self.queryset._clone()# Queryset is
Poll.objects.active().filter(event__enabled = True)
filtered_set = filtered_set.filter(event__id=event_id)
return render_to_response(template, filtered_set)

(this has been elided and adapted - original code is using django-rest-api,
JSON responder etc.  But the call boils down to this)

I'm confused as to what the problem could be - any clues?

Cheers,

Malcolm

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