Modify value of a Django form field during clean()

Question

I am adding custom validation to my forms and custom fields in my Django app. I would like to be able to modify the value of a field when triggering an error. For example, i

Answer 1

We can't redireclty edit request.data because it's an immutable dict. You need to copy it, do your stuff and return it.

But after differentes solutions I find this way (tested in Django 2.2.6)

class MyForm(ModelForm):

    def clean(self):
        cleaned_data = super(MyForm, self).clean()
        self.instance.field = 'value'
        return cleaned_data

Answer 2

If your form is a model form a better approach would be to get an instance and correct that data instead:

inst = my_form.save(commit=False)
if inst.a34_stuff is None: #or incorrect
    inst.a34_stuff = "corrected"
    request.user.message_set.create(message = "Error corrected")
    return HttpResponseRedirect(reverse('your_url_name',
            args=[])

PS: I am not sure if this will actually work... Not sure if form will pickup changes.

Answer 3

change self data in the clean method to change the value which gets displayed

Answer 4

It is possible to modify a value of a field during clean() if you update self.data attribute of a Form. self.data is an instance of the QueryDict class. By default, querydicts are immutable. To make them mutable, you should use .copy() method. From the documentation:

The QueryDicts at request.POST and request.GET will be immutable when accessed in a normal request/response cycle. To get a mutable version you need to use QueryDict.copy()

self.data = self.data.copy()
self.data['your_field'] = 'new value'

Answer 5

This is the way I've tried and works for me:

 inst = my_form.save(commit=False)
 if not inst.a34_stuff: # or incorrect
     inst.data["a34_stuff"] = "corrected"

Answer 6

I was setting a value to a specific field in another clean function, but it didnt work because of it was overwrited by the main clean function. In order to set the value and keep it :

• There didnt work.

    def clean_tipo_cupon(self):
        tipo_cupon = self.cleaned_data['tipo_cupon']
        qscu = mdlcat.TipoCuponVenta.objects.filter(
            id=tipo_cupon, estado_id=1,
        )
        if not qscu.exists():
            wmessage = u'introducido no paso validación'
            raise forms.ValidationError(wmessage)

        qscu = qscu.first()
        if not qscu.default_owner is None:
            self.cleaned_data['default_owner'] = qscu.default_owner.id

        return tipo_cupon

• Here, it worked like a charm.

    def clean(self):
        cleaned_data = super().clean()
        for item in self.fields.keys():
            if isinstance(cleaned_data.get(item), str):
                cleaned_data[item] = cleaned_data.get(item).upper()

        # if a default owner is configured by coupon type
        # it will be assigned
        tipo_cupon = cleaned_data['tipo_cupon']
        qscu = mdlcat.TipoCuponVenta.objects.filter(
            id=tipo_cupon, estado_id=1,
        )
        qscu = qscu.first()
        if not qscu.default_owner is None:
            self.cleaned_data['default_owner'] = qscu.default_owner.id

        return cleaned_data