disabled field is marked as required after passing null=True

Question

I have a form where there is a field like quantity, rate, basic_amount(disabled), vat, other_expenses and net_amount(disabled). The basic_amount field is the calculation from quantity and rate and net_amount is the calculation of basic_amount, other_expenses and vat. For this I used signal for saving to the database when user submits the form. When i submit the form, I get an error saying basic_amount and net_amount is required, though I have passed blank=True, null=True attribute to them.

How can i now save basic_amount and net_amount?

Here is my code

class PurchaseOrder(models.Model):
    item = models.ForeignKey(Item, blank=True, null=True)
    quantity = models.PositiveIntegerField(default=0)
    rate = models.DecimalField(default=0.0, max_digits=100, decimal_places=2)
    basic_amount = models.DecimalField(default=0.0, max_digits=100, decimal_places=2, blank=True, null=True)
    vat = models.CharField(max_length=10, blank=True, null=True)
    other_expenses = models.DecimalField(default=0.0, max_digits=100, decimal_places=2)
    net_amount = models.DecimalField(default=0.0, max_digits=100, decimal_places=2, blank=True, null=True)

def save_basic_amount_and_net_amount(sender, instance, *args, **kwargs):
    if (instance.quantity and instance.rate):
        instance.basic_amount = instance.quantity * instance.rate
    if (instance.basic_amount and instance.vat and instance.other_expenses):
        instance.net_amount = instance.amount - instance.other_expenses - instance.vat
pre_save.connect(save_basic_amount_and_net_amount, sender=PurchaseOrder)


class PurchaseOrderForm(forms.ModelForm):
    basic_amount = forms.DecimalField(disabled=True)
    net_amount = forms.DecimalField(disabled=True)
    class Meta:
        model = PurchaseOrder
        exclude = ('office', 'timestamp', 'updated', )

def purchase_order(request):
    form = PurchaseOrderForm(request.POST or None)
    if request.method == "POST" and form.is_valid():
        office_instance = OfficeSetup.objects.get(owner=request.user)
        new_form = form.save(commit=False)
        new_form.office = office_instance
        new_form.save()
        messages.success(request, 'Thank you')
        return redirect('purchase-order-lists')
    messages.warning(request, "Correct the errors below")
    context = {
        "form": form,
    }
    return render(request, 'dashboard/purchase_order/purchase_order.html', context)

Answer 1

blank=True and null=True relate to what is permissible in the database, not the form. If the value can be blank in the form, then add required=False to the form definition. For example:

class PurchaseOrderForm(forms.ModelForm):
    basic_amount = forms.DecimalField(disabled=True, required=False)
    ...