RelatedObjectDoesNotExist during form validation - django

Question

I have an issue that makes me crazy
I have model
class Property1(CommonInfo):
unit = models.ForeignKey(Unit)
is_true = models.BooleanField(default=False)
propertytype = models.ForeignKey(Propertytype, related_name='propertytype')
date = models.DateTimeField(null=True, blank=True)
followup_date = models.DateTimeField(null=True, blank=True)
quantity = models.PositiveSmallIntegerField()
def __str__(self):
return self.propertytype
def clean(self):
model = self.__class__
if (self.unit) and model.objects.filter(unit=self.unit, propertytype=self.propertytype ).exclude(id=self.id).count() == 1:
raise ValidationError('Same property cant be assigned more then ones')
for this model I have form
class Property1Form(forms.ModelForm):
class Meta:
model = Property1
fields = ['unit','propertytype','is_true','date','followup_date','quantity','description']
def __init__(self, *args, **kwargs):
super(Property1Form, self).__init__(*args, **kwargs)
instance = getattr(self, 'instance', None)
if instance:
self.fields['unit'].required = False
self.fields['unit'].widget.attrs['disabled'] = 'disabled'
And I have a view
def property_new(request,pk,uri):
unit = get_object_or_404(Unit, pk=pk)
title = 'property'
uri = _get_redirect_url(request, uri)
if request.method == "POST":
form = Property1Form(request.POST)
form.unit = unit
if form.is_valid():
properties = form.save(commit=False)
properties.unit = unit
properties.save()
messages.add_message(request, messages.SUCCESS, str(properties.unit) + "-SUCCESS Object created sucssefully")
return redirect(uri)
else:
form = Property1Form(initial={'unit': unit})
return render(request, 'object_edit.html', {'form': form, 'title':title, 'extend': EXTEND})
However, after creating new property I always get
RelatedObjectDoesNotExist at *** Property1 has no unit.
Error triggered during execution of
if form.is_valid():
What is the problem?
UPDATE:
Traceback:
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\core\handlers\base.py" in get_response
132. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:\Users\Boris\dev\rentout\rentout\unit\views.py" in property_new
390. if form.is_valid():
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\forms\forms.py" in is_valid
184. return self.is_bound and not self.errors
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\forms\forms.py" in errors
176. self.full_clean()
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\forms\forms.py" in full_clean
394. self._post_clean()
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\forms\models.py" in _post_clean
430. self.instance.full_clean(exclude=exclude, validate_unique=False)
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\db\models\base.py" in full_clean
1132. self.clean()
File "C:\Users\Boris\dev\rentout\rentout\unit\models.py" in clean
117. if (self.unit) and model.objects.filter(unit=self.unit, propertytype=self.propertytype ).exclude(id=self.id).count() == 1:
File "C:\Users\Boris\dev\rentout\virtrentout\lib\site-packages\django\db\models\fields\related.py" in __get__
608. "%s has no %s." % (self.field.model.__name__, self.field.name)
Exception Type: RelatedObjectDoesNotExist at /unit/property/new/6/http://127.0.0.1:8000/unit/property_details/6/
Exception Value: Property1 has no unit.

Answer 1

Setting required=False and disabling the widget is not ideal. Disabling the widget means that your browser will not submit any values for that field. Since you have required=False, this means that the form will set the foreign key to None. However, this is incompatible with the model's foreign key, which has null=False by default.
I'm not familiar enough with the internals to precisely explain the exception, but the basic problem is that Django is trying to fetch the related unit from the database, after the form has set the foreign key to None.
One work around is to check self.unit_id rather than self.unit. This prevents the database lookup, so you don't get the exception.
However, this seems a bit dirty to me. If you don't want the user to edit the unit field, I would remove it from the form completely. Check self.instance.pk to determine whether or not the instance is in the database already.
def __init__(self, *args, **kwargs):
super(Property1Form, self).__init__(*args, **kwargs)
if self.instance.pk:
del self.fields['unit']
Then in your view, you shouldn't have to set properties.unit = unit any more. I would remove form.unit = unit as well, I don't think it was ever useful.