Shoping cart M2M model with items count in Django - django

Question

I'm trying to create shopping cart system for one of mine pet project.
I have Profile model that is an extension for built-in User model. My Profile model has shopping_cart field which is M2M relationship to Clothing model from another app, which represents my product. In code, Profile model looks like this:
class Profile(models.Model):
user = models.OneToOneField(User, on_delete=models.CASCADE, related_name="profile")
...
shopping_cart = models.ManyToManyField(
to=Clothing,
related_name="shopping_cart",
blank=True
)
To add new item to shopping_cart field I use request object that has user object which in turn has profile that I need:
request.user.profile.shopping_cart.add(item)
So, I want to let user add multiple instances of the same item to shoping_cart, and then just count how many and what items do user has in his shopping_cart, probably, with Counter from collections.
Then, if I added let's say, 3 items to shopping_cart, I expecting output like this (with Counter from collections):
Counter({<Clothing: 14VQv52T2409iXGC7958>: 3})
But I got this:
Counter({<Clothing: 14VQv52T2409iXGC7958>: 1})
Now, who can explain why this happens, because I thought M2M means I can add multiple instances of same item, and it will display ALL added items.
UPD 1:
Intermediate model:
class ShoppingCart(models.Model):
item = models.ForeignKey(to=Clothing, on_delete=models.CASCADE)
in_profile = models.ForeignKey(to="Profile", on_delete=models.CASCADE)
count = models.PositiveSmallIntegerField(
default=1,
blank=False,
null=False
)
def __str__(self):
return self.item.title
Part where I proceeding request:
def proceed_request(self, request):
item = Clothing.objects.get(pk=request.POST.get("id"))
related_field = request.user.profile.shopping_cart
if item and item in related_field.all():
related_field.count() += 1 # Throws 'SyntaxError: can't assign to function call' error.
related_field.save()
messages.add_message(request, messages.SUCCESS, f"{item.title} has successfully uppdated!")
return HttpResponse(status=200)
related_field.add(item)
messages.add_message(request, messages.SUCCESS, f"{item.title} has successfully added to {self.verbose_field_name}!")
return HttpResponse(status=200)
UPD 2:
Updated proceed_request function. now all works well.
def proceed_request(self, request):
item = Clothing.objects.get(pk=request.POST.get("id"))
related_model = request.user.profile.shopping_cart
if item and item in related_model.all():
cart_item = ShoppingCart.objects.get(item=item)
cart_item.count += 1
cart_item.save()
messages.add_message(request, messages.SUCCESS, f"{item.title} has successfully uppdated!")
return HttpResponse(status=200)
ShoppingCart.objects.create(item=item, in_profile=request.user.profile)
messages.add_message(request, messages.SUCCESS, f"{item.title} has successfully added to {self.verbose_model_name}!")
return HttpResponse(status=200)

Answer 1

With M2M you can add multiple different items of Clothing, but adding the same item multiple times will not duplicate the relation. Have a look at adding a count field to the relation by using through:
https://docs.djangoproject.com/en/3.0/topics/db/models/#extra-fields-on-many-to-many-relationships