Hello,
- python version: 3.7
- django version: 2.2.16
After upgrading django from 2.2.15 to 2.2.16, I am experiencing errors with
the code shown below (see ----code----). Since 2.2.16 the
"getattr(self.original, field_name)" line results in the following stack
trace, which did not happen in 2.2.15:
--------stack trace---------
File "/app/src/contrib/changed_model_fields/mixins.py", line 20, in save
self.has_changed_fields(related_model)
File "/app/src/contrib/changed_model_fields/mixins.py", line 44, in
has_changed_fields
print(getattr(self.original, field_name))
File
"/usr/local/lib/python3.7/site-packages/django/db/models/fields/related_descriptors.py",
line 189, in __get__
"%s has no %s." % (self.field.model.__name__, self.field.name)
src.core.models.Variant.product.RelatedObjectDoesNotExist: Variant has no
product.
--------stack trace---------
The purpose of the "ChangedFieldMixin" is to determine if it contains any
modified (changed) attributes. The patch notes of 2.2.16
<https://docs.djangoproject.com/en/3.1/releases/2.2.16/> mentions
something, which I believe to be related to my issue:
https://code.djangoproject.com/ticket/31863
----------code------------
from copy import copy
class ChangedFieldMixin(object):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.original = copy(self)
def save(self, related_model: ModelType = None, *args, **kwargs):
force_changed_field = kwargs.pop('force_changed_field', False)
if self.has_changed_fields(related_model):
...
super().save(*args, **kwargs)
def has_changed_fields(self, related_model: ModelType):
for field in self._meta.fields:
field_name = str(field.name)
if not getattr(self, field_name) == getattr(self.original,
field_name):
return True
return False
class Variant(ChangedFieldMixin, models.Model):
product = models.ForeignKey('Product', on_delete=models.CASCADE)
code = models.CharField(max_length=255, null=True, blank=True)
name = models.CharField(max_length=255, null=True, blank=True)
key = models.CharField(max_length=255, unique=True, null=False,
blank=False)
quantity = models.PositiveIntegerField(null=True, blank=True)
default_price = models.PositiveIntegerField(default=None, null=True,
blank=True)
----------code------------
Is this expected behaviour now, or did the patch introduce a bug? Let me
know if I can provide additional information for the subject.
Thanks in advance
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