#33011: my_model.manyrelation_set.all() return empty value
-------------------------------------+-------------------------------------
Reporter: Floréal Cabanettes | Owner: nobody
Type: Bug | Status: new
Component: Database layer | Version: 3.2
(models, ORM) |
Severity: Normal | Resolution:
Keywords: model set querying | Triage Stage:
| Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
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Comment (by Floréal Cabanettes):
Hi,
I found the commit responsible for this bug:
{{{
036f160733 ("Refs #20577 -- Deferred filtering of prefetched related
querysets by reverse m2o relation.", 2020-10-06)
}}}
The line which cause the problem is on the file
django/db/models/fields/related_descriptors.py, line 584 (581 at the
commit, 584 on tag 3.2.6) :
{{{
queryset._defer_next_filter = True
}}}
If I comment this line, the bug disappear.
My code is not public (is for my enterprise, not my choice). I try to
describe a similar architecture bellow:
I have 2 models, one is "Run", the other "Experiment", related by a
OneToMany relationship:
{{{
class Run(model.Model):
label = models.CharField(max_length=100, null=False, blank=False)
owner = models.ForeignKey(User, null=True, blank=True,
on_delete=models.PROTECT, related_name="run_owner")
class Experiment(model.Model):
run = models.ForeignKey(Run, null=False, on_delete=models.PROTECT)
index1 = models.ForeignKey(Index, null=False,
on_delete=models.PROTECT, related_name="index1")
index2 = models.ForeignKey(Index, null=True, blank=True,
on_delete=models.PROTECT, related_name="index2")
}}}
I use the django rest framework to call the server through REST API. For
one endpoint, I get a run, and I try to get it's experiments, to then make
a copy of them:
{{{
@action(detail=True, methods=["post"])
def copy(self, request, pk=None):
try:
my_run = self.get_queryset().get(pk=pk)
except ObjectDoesNotExist:
return Response({"detail": _("Run with id '%s' does not exists") %
pk},
status=status.HTTP_404_NOT_FOUND)
my_experiments = my_run.experiment_set.all()
for my_experiment in my_experiments:
my_experiment.pk = None
...
my_experiment.save()
}}}
and the problem is that `my_experiments` is empty with django 3.2.6 (and
no more empty with the line commented like said before).
I hope this will help to solve the problem...
--
Ticket URL: <https://code.djangoproject.com/ticket/33011#comment:2>
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