Execute validate_unique when form doesn’t include all fields

Asked this question on Stack Overflow today:

https://stackoverflow.com/questions/48449821/execute-validate-unique-when-form-doesnt-include-all-fields

I recently had a situation where the validate_unique method from my model wasn’t running. This is because one of the fields involved in the unique test wasn’t included in the form. I tried many things in the form and the view before landing on this solution: I first injected the field into the object of the UpdateView, then ran the test in the Form in _post_clean.

models.py 

class Link(ModelBase):
	id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
	title = models.CharField(max_length=200,blank=True,null=False)
	url = models.URLField(max_length=400,blank=False,null=False)
	profile = models.ForeignKey('Profile',null=False,blank=False,on_delete=models.CASCADE)

	class Meta:
		unique_together = ('url','profile')

	class Admin:
		pass

forms.py 

class LinkForm(ModelForm):

	def _post_clean(self):
		''' Be sure that the instance validate_unique method is run including the profile field '''
		super(LinkForm,self)._post_clean()
		try:
			self.instance.validate_unique(exclude=None)
		except ValidationError as e:
			self._update_errors(e)

	class Meta:
		model = Link
		fields = ['title','url']

views.py 

class LinkUpdateView(UpdateView):
	model = Link
	form_class = LinkForm

	def get_form_kwargs(self):
		''' Add profile to self.object before kwargs are populated '''

		if hasattr(self, 'object') and self.object and self.profile:
				self.object.profile = profile

		kwargs = super(LinkUpdateView, self).get_form_kwargs()

		return kwargs

Is there a better way to do this that doesn’t involve overriding an internal function?

Got any help for me? Please post an answer here or on SO. I’ll share the solution here once I get one.