Django: Cart matching query does not exist - django

Question

I've a form that creates a Cart with the text "Random" in a character field, if there is not a Cart object created. This is only to get this recently object's id if it is not already created.
cart = Cart.objects.get(id=cart_id)
I get an error saying that this query generates an error, however I can see the value of cart_id as a cookie so the Query should execute without problem. But it doesn't according to the error message.
Exception Type: DoesNotExist
Exception Value: Cart matching query does not exist.
As you can see in my view, I'm using this:
cart_id = self.request.COOKIES.get('cart_id')
if not cart_id:
cart = Cart.objects.create(cart_id="Random")
cart_id = cart.id
cart = Cart.objects.get(id=cart_id)
To get the cookie cart_id if it does not exist I created a Cart object with the Random text, only to get it's ID.
Why I'm getting the error?
View.py:
class StepOneView(FormView):
form_class = StepOneForm
template_name = 'shop/medidas-cantidades.html'
success_url = 'subir-arte'
def get_initial(self):
# pre-populate form if someone goes back and forth between forms
initial = super(StepOneView, self).get_initial()
initial['size'] = self.request.session.get('size', None)
initial['quantity'] = self.request.session.get('quantity', None)
initial['product'] = Product.objects.get(
category__slug=self.kwargs['c_slug'],
slug=self.kwargs['product_slug']
)
return initial
def get_context_data(self, **kwargs):
context = super().get_context_data(**kwargs)
context['product'] = Product.objects.get(
category__slug=self.kwargs['c_slug'],
slug=self.kwargs['product_slug']
)
return context
def form_invalid(self, form):
print('Step one: form is NOT valid')
def form_valid(self, form):
cart_id = self.request.COOKIES.get('cart_id')
if not cart_id:
cart = Cart.objects.create(cart_id="Random")
cart_id = cart.id
cart = Cart.objects.get(id=cart_id)
item = CartItem.objects.create(
size=form.cleaned_data.get('size'),
quantity=form.cleaned_data.get('quantity'),
product=Product.objects.get(
category__slug=self.kwargs['c_slug'],
slug=self.kwargs['product_slug']
),
cart=cart
)
response = HttpResponseRedirect(self.get_success_url())
response.set_cookie("cart_id", cart_id)
response.set_cookie("item_id", item.id)
return response
models.py:
class Cart(models.Model):
cart_id = models.CharField(max_length=100)
date_added = models.DateField(auto_now_add=True)
class Meta:
db_table = 'Cart'
ordering = ['date_added']
def __str__(self):
return str(self.id)

Answer 1

Try this:
def form_valid(self, form):
cart_id = self.request.COOKIES.get('cart_id')
if cart_id:
try:
cart = Cart.objects.get(id=cart_id)
except ObjectDoesNotExist:
# supplied ID doesn't match a Cart from your BD
cart = Cart.objects.create(cart_id="Random")
else:
cart = Cart.objects.create(cart_id="Random")
No need to create the Cart objects, just to get its ID and they hit the DB again to retrieve the same instance.
The idea is:
Do you have cart_id on session cookies? If so, try to get the Cart object based on it.
If that fails, it means that the supplied cart_id doesn't match an object from your DB
If no cart_id on session cookies, then simply create your new Cart object.