CODEWITHSUNDEEP
pythondjangodjango-forms
bdoubleu
bdoubleu

Reputation: 6127

Django: validate by field excluded from ModelForm

Can you validate a model form field by comparing it to an excluded field? How should the excluded field be set on init?

class MyModel(models.Model):
    amount = models.DecimalField()
    balance = models.DecimalField()

class MyForm(forms.ModelForm):
    def __init__(self, *args, **kwargs)
        self.balance = ??
        super(MyForm, self).__init__(*args, **kwargs)

    class Meta:
        model = MyModel
        fields = ['amount']

    def clean_amount(self):
        amount = self.cleaned_data['amount']
        if not (self.balance > 0 and amount > 0) or (self.balance < 0 and amount < 0):
            raise forms.ValidationError(
                'Cannot apply a negative amount to a positive balance and vice versa.')
        return amount

Upvotes: 1

Views: 125

Answers (1)

Alasdair
Alasdair

Reputation: 309099

Instantiate the form with the instance you are editing:

instance = MyModel.objects.get(pk=pk)
form = MyForm(instance=instance, data=request.POST)

Then in the form, you can access the balance via self.instance. You don't need to set self.balance in the __init__ method.

def clean_amount(self):
    amount = self.cleaned_data['amount']
    if not (self.instance.balance > 0 and amount > 0) or (self.instance.balance < 0 and amount < 0)
        raise forms.ValidationError(
            'Cannot apply a negative amount to a positive balance and vice versa.')
    return amount

Upvotes: 1

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