Django CreateView - created_by, modified_by mixin not working - django

Question

I have followed spapas tutorial on CBV's and tried to apply a mixin on a create view. But looks like it doesn't evaluate correctly the if not form.invoice.requester for a user foreign key because it always says: RelatedObjectDoesNotExist and it points to the field evaluated in the if not line.
What can be wrong?
views.py
class AuditableMixin(object, ):
def form_valid(self, form, ):
if not form.instance.requester:
form.instance.requester = self.request.user
form.instance.modified_by = self.request.user
return super().form_valid(form)
class NewOrderView(LoginRequiredMixin, PermissionRequiredMixin, AuditableMixin, generic.CreateView):
permission_required = 'orders.add_order'
form_class = NewOrderForm
model = Order
title = 'New Order'
extra_context = {'title': title}
forms.py
class NewOrderForm(forms.ModelForm):
class Meta:
model = Order
widgets = {
'order_details': forms.Textarea,
}
exclude = (
'status',
'invoice',
'requester',
'modified_by',
)
models.py
class Order(models.Model):
STATUS_CHOICES = (
('open', 'Open'),
('inprogress', 'In Progress'),
('rejected', 'Rejected'),
('closed','Closed'),
('resolved','Resolved'),
)
subject = models.CharField(
max_length=30,
)
requester = models.ForeignKey(
User,
on_delete=models.PROTECT,
related_name='orders',
)
order_details = models.TextField(
)
created = models.DateTimeField(
auto_now_add=True,
)
updated = models.DateTimeField(
auto_now=True,
)
status = models.CharField(
max_length=12,
default='open',
choices= STATUS_CHOICES,
)
invoice = models.ForeignKey(
Invoice,
on_delete=models.PROTECT,
blank= True,
null=True,
related_name='orders',
)
modified_by = models.ForeignKey(
User,
on_delete=models.PROTECT,
related_name='orders_modified',
)
def __str__(self):
return self.subject
def get_absolute_url(self):
return reverse('Order_Detail', args=[str(self.pk)])
class Meta:
ordering = ['-created']
Thank you.

Answer 1

When calling the ForeignKey object on a model, you're actually telling Django to perform the query to fetch the related object. To check if the relationship exists, you should check <fieldname>_id which is the actual name of the field:
if not form.instance.requester_id:
form.instance.requester = self.request.user
That way if requester_id is None you don't perform the query, which would through the RelatedObjectDoesNotExist error.