Django how to maintain a session? - django-sessions

Question

I'm developing an e-commerce site and I'm working on the shopping cart functionality. When the user is not connected I create a session for him so that he can add products to the basket which is normal, when the user decides to place this order I ask him to connect but when he connects he loses the session that I had created for him and another session is assigned to him. The cause is that once connected it loses all its products selected in the screen. After reading the documentation on django sessions I found nothing that could help me.
here is my code for more details:
models.py
class Cart(models.Model):
session_id = models.CharField(max_length=150)
product = models.ForeignKey(Products, on_delete=models.CASCADE)
quantity = models.PositiveIntegerField(default=0, validators=[MinValueValidator(1)])
updated = models.fields.DateTimeField(auto_now=True)
created = models.fields.DateTimeField(auto_now_add=True)
deleted = models.fields.BooleanField(default=False)
def __str__(self) -> str:
return str(self.product)
views.py
class FrontProductAddCart(View):
def post(self, request, product_pk):
session_id = request.session._get_or_create_session_key()
product = models.Products.objects.get(pk=product_pk)
objet, create = models.Cart.objects.get_or_create(session_id=session_id, product=product)
quantity = request.POST.get("quantity")
if quantity:
objet.quantity = quantity
objet.save()
else:
objet.quantity += 1
objet.save()
return HttpResponse(
"",
headers={
"HX-Trigger": json.dumps({
"product_add_cart": context_processors.get_total_number_products(request)
})
}
)