Passing an argument from views to Form Validation - django

Question

Is there a way I can get the product gotten from product = Product.objects.get(id=id) and use it in my form validation? In my template, I have listed all my products and each has the AddSaleForm. When the user fills the form and submits it sends them to the make_sale view. Now I need to check that the quantity entered from the form does not exceed the quantity each product has (as shown in my commented code in my FORMS.PY.)
Is there a way I can get the product?
MY FORMS.PY
class AddSaleForm(forms.ModelForm):
class Meta:
model = Sale
fields = ['quantity', 'selling_price']
widgets = {
'quantity': NumberInput(attrs={'class': 'form-control', 'placeholder': 'items number'}),
'selling_price': NumberInput(attrs={'class': 'form-control', 'placeholder': '1000.00'}),
}
def clean_quantity(self, *args, **kwargs):
sale_quantity = self.cleaned_data.get('quantity')
if sale_quantity == 0:
raise forms.ValidationError('The sale quantity cannot be zero (0)')
# elif sale_quantity > product_quantity: # <----rom the product accessed from make_sale view
# raise forms.ValidationError('The sale quantity cannot exceed the available quantity. '
# 'The availabe quantity for this product is ' + str(product_quantity))
return sale_quantity
MY VIEWS.PY
def make_sale(request, id):
product = Product.objects.get(id=id) # To be accessed in the form for validation
if request.method == 'POST':
form = AddSaleForm(request.POST)
if form.is_valid():
quantity = form.cleaned_data['quantity']
selling_price = form.cleaned_data['selling_price']
Sale.objects.create(product=product, quantity=quantity, selling_price=selling_price, sold_by=request.user)
product_quantity = product.quantity
sale_no = product.number_of_sales
new_sale = sale_no + 1
new_quantity = product_quantity - quantity
Product.objects.filter(id=product.id).update(quantity=new_quantity, number_of_sales=new_sale)
messages.success(request, str(quantity) + ' ' + 'item(s) sale for ' + str(product.name) + ' at Kshs. '
+ str(selling_price) + ' made successfully!')
return redirect(reverse('products:todays_sales'))

Answer 1

I don't know if this is a good idea to send other object to non related model form but one way is to send Product instance to your form and then use it's attributes in clean method of your AddSaleForm. Something like following code:
Goes in your views ->
product = Product.objects.get(id=id)
form = AddSaleForm(request.POST or None, initial={'product_instance': product})
And then in your clean method of AddSaleForm you have access to that instance. Following code may help you to understand what I'm saying:
Goes in your forms ->
class AddSaleForm(forms.ModelForm):
model = Sale
fields = ['quantity', 'selling_price']
widgets = {
'quantity': NumberInput(attrs={'class': 'form-control', 'placeholder': 'items number'}),
'selling_price': NumberInput(attrs={'class': 'form-control', 'placeholder': '1000.00'}),
}
def clean(self):
super().clean()
product_instance = self.initial['product_instance']
# You can add your conditions based on product instance here