Django's ModelForm unique_together validation

user_208706 0
Viewed 24907

I have a Django model that looks like this.

class Solution(models.Model):
    '''
    Represents a solution to a specific problem.
    '''
    name = models.CharField(max_length=50)
    problem = models.ForeignKey(Problem)
    description = models.TextField(blank=True)
    date = models.DateTimeField(auto_now_add=True)

    class Meta:
        unique_together = ("name", "problem")

I use a form for adding models that looks like this:

class SolutionForm(forms.ModelForm):
    class Meta:
        model = Solution
        exclude = ['problem']

My problem is that the SolutionForm does not validate Solution's unique_together constraint and thus, it returns an IntegrityError when trying to save the form. I know that I could use validate_unique to manually check for this but I was wondering if there's any way to catch this in the form validation and return a form error automatically.

Thanks.

modelform validation django
10 Answers

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.

user_2087060

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?

user_1043490

You will need to do something like this:

def your_view(request):
    if request.method == 'GET':
        form = SolutionForm()
    elif request.method == 'POST':
        problem = ... # logic to find the problem instance
        solution = Solution(problem=problem) # or solution.problem = problem
        form = SolutionForm(request.POST, instance=solution)
        # the form will validate because the problem has been provided on solution instance
        if form.is_valid():
            solution = form.save()
            # redirect or return other response
    # show the form
user_2596760

My solution is based off Django 2.1

Leave SolutionForm alone, have a save() method in Solution

class Solution(models.Model):
...
   def save(self, *args, **kwargs):
      self.clean()
      return super(Solution, self).save(*args, **kwargs)


  def clean():
      # have your custom model field checks here
      # They can raise Validation Error

      # Now this is the key to enforcing unique constraint
      self.validate_unique()

Calling full_clean() in save() does not work as the ValidationError will be unhandled

user_111025070

I needed to exclude the company field in my case and add it in the view's form_valid function. I ended up doing the following (taking inspiration from different answers). In my CreateView

    def form_valid(self, form):
        cleaned_data = form.cleaned_data
        user_company = self.request.user.profile.company
        if UnitCategory.objects.filter(code=cleaned_data['code'],
                                    company=user_company).exists():
            form.add_error('code',                           _(
                'A UnitCategory with this Code already exists for this company.'))
            return super(UnitCategoryCreateView, self).form_invalid(form)
        if UnitCategory.objects.filter(color=cleaned_data['color'],
                                    company=user_company).exists():
            form.add_error('color',                           _(
                'A UnitCategory with this Color already exists for this company.'))
            return super(UnitCategoryCreateView, self).form_invalid(form)
        form.instance.company = user_company
        return super(UnitCategoryCreateView, self).form_valid(form)

In my UpdateView I had to exclude the current instance of the object in checking if the query exist using exclude(pk=self.kwargs['pk'])

    def form_valid(self, form):
        cleaned_data = form.cleaned_data
        user_company = self.request.user.profile.company
        if UnitCategory.objects.filter(code=cleaned_data['code'],
                                       company=user_company).exclude(pk=self.kwargs['pk']).exists():
            form.add_error(
                'code', _('A UnitCategory with this Code already exists for this company.'))
            return super(UnitCategoryUpdateView, self).form_invalid(form)
        if UnitCategory.objects.filter(color=cleaned_data['color'],
                                       company=user_company).exclude(pk=self.kwargs['pk']).exists():
            form.add_error('color', _(
                'A UnitCategory with this Color already exists for this company.'))
            return super(UnitCategoryUpdateView, self).form_invalid(form)
        # Return form_valid if no errors raised
        # Add logged-in user's company as form's company field
        form.instance.company = user_company
        return super(UnitCategoryUpdateView, self).form_valid(form)

Not the cleanest solution I was hoping for, but thought it might benefit someone.

user_41574310

If you always want to check the uniqueness constraint (i.e. on every ModelForm you create), you can make sure the uniqueness constraint is always validated on the model:

# Always check name-problem uniqueness
def validate_unique(self, exclude=None):
    if exclude is None:
        exclude = []

    try:
        exclude.remove("problem")
    except ValueError:
        pass

    return super().validate_unique(exclude)

This works because the model's validate_unique method is called during form validation.

user_173768730
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