Django's ModelForm unique_together validation

I solved this same problem by overriding the validate_unique() method of the ModelForm:

def validate_unique(self):    exclude = self._get_validation_exclusions()    exclude.remove('problem') # allow checking against the missing attribute    try:        self.instance.validate_unique(exclude=exclude)    except ValidationError, e:        self._update_errors(e.message_dict)

Now I just always make sure that the attribute not provided on the form is still available, e.g. instance=Solution(problem=some_problem) on the initializer.

As Felix says, ModelForms are supposed to check the unique_together constraint in their validation.

However, in your case you are actually excluding one element of that constraint from your form. I imagine this is your problem - how is the form going to check the constraint, if half of it is not even on the form?

I managed to fix this without modifying the view by adding a clean method to my form:

class SolutionForm(forms.ModelForm):    class Meta:        model = Solution        exclude = ['problem']    def clean(self):        cleaned_data = self.cleaned_data        try:            Solution.objects.get(name=cleaned_data['name'], problem=self.problem)        except Solution.DoesNotExist:            pass        else:            raise ValidationError('Solution with this Name already exists for this problem')        # Always return cleaned_data        return cleaned_data

The only thing I need to do now in the view is to add a problem property to the form before executing is_valid.