#26522: Bug in django.db.models.sql.Query.combine
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Reporter: OleLaursen | Owner: nobody
Type: Bug | Status: new
Component: Database layer (models, ORM) | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Easy pickings: 0 | UI/UX: 0
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Hi,
There's a logical error somewhere in Query.combine or friends.
I have a pretty complicated query with many-to-many self-joins and ORs,
and after the upgrade to Django 1.9 and Python 3 combine() sometimes, but
not always, crashes with the assertion error
{{{
assert set(change_map.keys()).intersection(set(change_map.values())) ==
set()
}}}
Inspecting the change_map, it does indeed contain a circular reference
(BTW shouldn't you use "not" to test for an empty set rather than
comparing with set()?).
At first, I didn't understand how it could crash sometimes and sometimes
not - we're talking about the same query being executed through a view.
But when I examine change_map, its content does indeed change from reload
to reload - I suppose this may have something to do with the order of
dicts/sets the combine() algorithm is using.
Here comes some code, I cut out a bunch of unused stuff, but otherwise
it's the same:
{{{
class Invoice(models.Model):
customer = models.ForeignKey(Customer)
date_created = models.DateField(default=datetime.date.today,
db_index=True)
date_sent = models.DateField(null=True, blank=True)
date_due = models.DateField(null=True, blank=True)
date_paid = models.DateField(null=True, blank=True)
date_credited = models.DateField(null=True, blank=True)
date_collect = models.DateField(null=True, blank=True)
invoice_type = models.CharField(default="invoice", max_length=32)
reminders = models.ManyToManyField("Invoice",
related_name="reminded_set", blank=True)
reminder_counter = models.IntegerField(null=True, blank=True)
}}}
That's the model, and in the view:
{{{
import datetime
from django.db.models import Q
date = datetime.datetime.now()
invoices = Invoice.objects.filter(
Q(date_created__lte=date),
Q(date_paid__gt=date) | Q(date_paid=None),
Q(date_credited__gt=date) | Q(date_credited=None),
customer=1,
)
filtered_invoices = Invoice.objects.none()
not_due = Q(date_due__gte=date) | Q(date_due=None)
not_reminded_yet = ~Q(reminders__date_created__lte=date)
not_collected = Q(date_collect__gt=date) | Q(date_collect=None)
filtered_invoices |= invoices.filter(not_due, not_collected,
date_sent__lte=date, invoice_type="invoice")
filtered_invoices |= invoices.filter(not_collected, not_reminded_yet,
date_sent__lte=date, date_due__lt=date, invoice_type="invoice")
for r in [1, 2, 3]:
qs = invoices.filter(not_collected,
reminders__date_created__lte=date, reminders__reminder_counter=r,
invoice_type="invoice")
for i in range(r + 1, 3 + 1):
qs = qs.filter(~Q(reminders__reminder_counter=i) |
Q(reminders__reminder_counter=i, reminders__date_created__gt=date))
filtered_invoices |= qs
}}}
I realize it's pretty complicated but I'm not sure what's essential and
what's not. I hope someone knowledgeable of how combine() works can figure
out why ordering in some cases matters.
--
Ticket URL: <https://code.djangoproject.com/ticket/26522>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
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