How to update specific model fields using Django UpdateView - django

Question

How can you update certain model fields when a form is posted using Django's UpdateView?
When the user checks complete = True on the form, and submits it, I want their name and date to be saved to this record (fields not visible on the form). The code below isn't throwing any errors, but it also isn't updating the fields requested.
Is it potentially because the view is already updating this record with the form, so they conflict?
view:
class maintenanceEdit(LoginRequiredMixin,UpdateView,):
model = Maintenance
form_class = EditMaintenance
template_name = 'maintenance_edit.html'
login_url = 'login'
success_url = reverse_lazy('equipmentdashboard')
def form_valid(self, form,):
instance = form.save(commit=False)
instance.user = self.request.user
user = instance.user.first_name +" "+instance.user.last_name
completed = form.instance.completed
dateCompleted = form.instance.dateCompleted
if (dateCompleted is None):
if completed == True:
updateMaintenance = Maintenance.objects.get(id = instance.id)
updateMaintenance.dateCompleted = timezone.now()
updateMaintenance.completedBy = user
updateMaintenance.save(update_fields=['dateCompleted','completedBy',])
return super(maintenanceEdit, self).form_valid(form)
model:
class Maintenance(models.Model):
device = models.ForeignKey(get_user_model(),on_delete=models.CASCADE,)
customerTag = models.CharField(max_length=50,)
maintenanceItem = models.CharField(max_length=35,blank=True,)
maintenanceDescrip = models.TextField(max_length=300,blank=True,)
maintenanceNotes = models.TextField(max_length=300,blank=True,)
dateCreated = models.DateTimeField(auto_now_add=True,)
dateDue = models.DateTimeField(auto_now=False, auto_now_add=False, null=True, blank=True, editable=True)
dateCompleted = models.DateTimeField(auto_now=False, auto_now_add=False, null=True, blank=True, editable=True)
completed = models.BooleanField(default = False)
createdBy = models.CharField(max_length=35,blank=True,)
completedBy = models.CharField(max_length=35,blank=True,)
form:
class EditMaintenance(forms.ModelForm):
def __init__(self, *args, **kwargs):
super(EditMaintenance, self).__init__(*args, **kwargs)
self.fields['maintenanceItem'].required = True
self.fields['dateDue'].required = True
class Meta:
model = Maintenance
fields = ['maintenanceItem','dateDue','maintenanceDescrip',
'maintenanceNotes','completed',]
labels = {
'maintenanceItem': ('Maintenance Item'),
'dateDue': ('Maintenance Due'),
'maintenanceDescrip': ('Maintenance Description'),
'maintenanceNotes': ('Maintenance Notes'),
'completed': ('Complete Maintenance'),
}
I also tried, in my view:
def form_valid(self, form,):
instance = form.save(commit=False)
instance.user = self.request.user
user = instance.user.first_name +" "+instance.user.last_name
completed = form.instance.completed
dateCompleted = form.instance.dateCompleted
if (dateCompleted is None):
if completed == True:
Maintenance.objects.filter(id = instance.id).update(dateCompleted = timezone.now(),completedBy = user)
return super(maintenanceEdit, self).form_valid(form)