Form fields are empty when created using instance = instance - django

Question

I have two models prodcut_prices and WrongPrice.
In WrongPrice the user can correct report wrong prices - when the price is reported it should also be updated in product_price.
My problem is, even though I instantiate product_price at the very beginning as instance_productprice, all of its required fields returns the "this field has to be filled out" error.
How come those field are not set when im using the instance instance_productprice = product_prices.objects.filter(id=pk)[0] ? Note, that all fields in product_prices are always non-empty since they are being pulled from the product_price model, which is handled in another view, thus that is not the issue.
def wrong_price(request,pk):
#Get the current price object
instance_productprice = product_prices.objects.filter(id=pk)[0]
#Get different values
wrong_link = instance_productprice.link
img_url = instance_productprice.image_url
wrong_price = instance_productprice.last_price
domain = instance_productprice.domain
# Create instances
instance_wrongprice = WrongPrice(
link=wrong_link,
correct_price=wrong_price,
domain = domain)
if request.method == "POST":
form_wrong_price = wrong_price_form(request.POST,instance=instance_wrongprice)
# Update values in product_prices
form_product_price = product_prices_form(request.POST,instance=instance_productprice)
form_product_price.instance.start_price = form_wrong_price.instance.correct_price
form_product_price.instance.last_price = form_wrong_price.instance.correct_price
if form_wrong_price.is_valid() & form_product_price.is_valid():
form_wrong_price.save()
form_product_price.save()
messages.success(request, "Thanks")
return redirect("my_page")
else:
messages.error(request, form_product_price.errors) # Throws empty-field errors,
messages.error(request, form_wrong_price.errors)
return redirect("wrong-price", pk=pk)
else:
form_wrong_price = wrong_price_form(instance=instance_wrongprice)
return render(request, "my_app/wrong_price.html",context={"form":form_wrong_price,"info":{"image_url":img_url}})

Answer 1

I am bit confused about how you implemented it. You have passed a instance of WrongPrice price through the form, which is unnecessary, you could have used initial:
wrong_values = dict(
link=wrong_link,
correct_price=wrong_price,
domain = domain
)
form_wrong_price = wrong_price_form(initial= wrong_values)
Then you are adding values to product_prices_form from instance of form_wrong_price. I don't see why you need a form again here. You can simple use:
form_wrong_price = wrong_price_form(request.POST, initial= wrong_values)
if form_wrong_price.is_valid():
instance = form_wrong_price.save()
instance_productprice.start_price = instance.correct_price
instance_productprice.last_price = instance.correct_price
instance_productprice.save()
Finally, please use PascalCase when defining class names. And you can get the product prices by product_prices.objects.get(id=pk)(instead of filter()[0]).