#31435: RecursionError when deleting a model with one to many relationship
-------------------------------------+-------------------------------------
Reporter: Fabian | Owner: nobody
Allendorf |
Type: Bug | Status: new
Component: Database | Version: 3.0
layer (models, ORM) | Keywords:
Severity: Normal |
delete,model,recursion,stack,overflow,reference,foreign,key,one,to,many
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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This issue appeared with upgrade from Django 2 to Django 3.0. I double
checked and it definitely works with version <3.0.
There is a model with a duration field and the "__init__" method is
overridden to save "old" values of this duration field.
{{{
class TimeSeries(models.Model):
frequency = models.DurationField()
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self._old_frequency = self.frequency
}}}
Another model extends this "TimeSeries" model and has a foreign key
reference to the model which I tried to delete.
{{{
class RefModel(TimeSeries):
main_model = models.ForeignKey(
MainModel, on_delete=models.CASCADE, related_name="refs"
)
class MainModel(models.Model):
pass
}}}
So I created an instance of "MainModel" "main_a" and added some "RefModel"
instances with relationhip to "main_a".
When I call "main_a.delete()" it ends up in a stack overflow with the
following stacktrace:
{{{
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "/lib/python3.8/site-packages/django/db/models/base.py", line 937,
in delete
collector.collect([self], keep_parents=keep_parents)
File "/lib/python3.8/site-packages/django/db/models/deletion.py", line
244, in collect
if sub_objs:
File "/lib/python3.8/site-packages/django/db/models/query.py", line 280,
in __bool__
self._fetch_all()
File "/lib/python3.8/site-packages/django/db/models/query.py", line
1261, in _fetch_all
self._result_cache = list(self._iterable_class(self))
File "/lib/python3.8/site-packages/django/db/models/query.py", line 75,
in __iter__
obj = model_cls.from_db(db, init_list,
row[model_fields_start:model_fields_end])
File "/lib/python3.8/site-packages/django/db/models/base.py", line 512,
in from_db
new = cls(*values)
File "/lib/python3.8/site-packages/django_timeseries/models.py", line
27, in __init__
self._old_frequency = self.frequency
File "/webserver/business_rules/thread_safe_model_patcher.py", line 51,
in _patched_get_attribute
return Model.get(model_self, item)
File "/lib/python3.8/site-packages/django/db/models/query_utils.py",
line 139, in __get__
instance.refresh_from_db(fields=[field_name])
File "/lib/python3.8/site-packages/django/db/models/base.py", line 627,
in refresh_from_db
db_instance = db_instance_qs.get()
File "/lib/python3.8/site-packages/django/db/models/query.py", line 411,
in get
num = len(clone)
File "/lib/python3.8/site-packages/django/db/models/query.py", line 258,
in __len__
self._fetch_all()
File "/lib/python3.8/site-packages/django/db/models/query.py", line
1261, in _fetch_all
<--- Stacktrace repeats itself from here on --->
}}}
"django_timeseries" is a custom package which defines the "TimeSeries"
class.
"thread_safe_model_patcher.py" monkeypatches the "Model" class. It has no
effect on whether the error happens. I removed the this patch and it still
errors.
It seems to me that deleting "main_a" deletes all "RefModel" instances
related to it (like it should) but while doing this, it gets stuck
initializing the super class "TimeSeries" because the "__init__" accesses
the "frequency" field.
--
Ticket URL: <https://code.djangoproject.com/ticket/31435>
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