Single CPF but with Blank=True

Question

If I define

cpf = models.CharField(max_length=11, unique=True, null=True, blank=True)

It turns out that if I leave a record with the null value, when I try to save a second record, it accuses duplicate value.

How to get around this situation?

Answer 1

If you define unique=True means that you cannot repeat any value, even NULL. The solution to this problem is to make a check before saving, if any repeated returns error to the users.

In the forms.py you can do a check the following way:

class SeuModelForm(forms.ModelForm):

    class Meta():
        model = SeuModel

    def __init__(self, *args, **kwargs):
        super(SeuModelForm, self).__init__(*args, **kwargs)
        if 'instance' in kwargs:
            self.id = kwargs['instance'].id
        else:
            self.id = None

    def clean(self):
        cleaned_data = super(SeuModelForm, self).clean()
        cpf = cleaned_data.get('cpf')
        if cpf:
            try:
                SeuModel.objects.exclude(id=self.id).get(cpf=cpf)
            except (SeuModel.DoesNotExist):
                pass
            else:
                self.add_error('cpf', u'Este CPF já foi cadastrado')

UPDATING:

After doing a survey I found that the problem was not with Django, so the bank accepts yes more than one NULL. To solve this problem more simply, just return None if the field has not been completed.

class SeuModelForm(forms.ModelForm):

    class Meta():
        model = SeuModel

    def clean_cpf(self):
        return self.cleaned_data['cpf'] or None

Or better yet, directly in the method save() of the model:

def save(self, *args, **kwargs):
    if not self.cpf:
        self.cpf = None
    super(SeuModel, self).save(*args, **kwargs)