Django ModelManager not saving the model instance correctly - python-3.x

Question

I am working on an ecommerce project but my OrderManager() class does not saving the instance(i think)
When i am clicking on BOOK button i am getting this error which is defined in my view
order_amount = order_obj.total * 100
AttributeError: 'NoneType' object has no attribute 'total'
But when i refresh the page error goes way and order_obj.total * 100 is calculated, But my question is why i need to refresh the page again and again when i create a new order.
Here is my models.py
class OrderQuerySet(models.query.QuerySet):
def not_created(self):
return self.exclude(status='created')
class OrderManager(models.Manager):
def get_queryset(self):
return OrderQuerySet(self.model, using=self.db)
def create_or_get_order(self, product):
created = None
obj = None
qs = self.get_queryset().filter(product=product, active=True, status='created')
if qs.count() == 1:
obj = qs.first()
else:
self.model.objects.create(product=product)
created = True
return obj, created
class Order(models.Model):
order_id = models.CharField(max_length=120, blank=True)
product = models.ForeignKey(Product, on_delete=models.CASCADE)
total = models.PositiveIntegerField()
active = models.BooleanField(default=True)
objects = OrderManager()
class Meta:
ordering = ['-ordered_on', '-updated']
def __str__(self):
return self.order_id
def check_done(self): # check everything is correct before final checkout
order_id = self.order_id
total = self.total
if order_id and total > 0:
return True
return False
def mark_paid(self):
if self.check_done():
self.status = 'paid'
self.save()
return self.status
def pre_save_create_order_id(sender, instance, *args, **kwargs):
if not instance.order_id:
instance.order_id = unique_order_id_generator(instance)
pre_save.connect(pre_save_create_order_id, sender=Order)
def pre_save_order_total(sender, instance, *args, **kwargs):
"""calculate the product total while clicking on Book Button
(Still booking is not done you just clicked on Book button)"""
instance.total = instance.product.price
pre_save.connect(pre_save_order_total, sender=Order)
Views.py
def checkout_home_view(request, *args, **kwargs):
order_obj = None
order_amount = None
order_currency = None
order_id = None
slug = kwargs['slug']
product = Product.objects.get(slug=slug)
if product is not None:
# ****************** Here is problem ******************************
order_obj, order_create = Order.objects.create_or_get_order(product)
''' HERE I AM GETTING order_obj as None BUT WHEN I REFRESH ERROR GOES WAY '''
print('order_obj', order_obj) # printing None initally
order_amount = order_obj.total * 100
order_currency = 'INR'
order_id = order_obj.order_id
if request.method == 'POST':
'check that booking is done'
is_prepared = order_obj.check_done() # check_done() defined in Order model
if is_prepared:
client = razorpay.Client(auth=("xxx", "xxx"))
payment = client.order.create(dict(amount=order_amount, currency=order_currency))
if payment:
order_obj.mark_paid() # mark_paid() defined in Order model
order_obj.save()

Answer 1

class OrderManager(models.Manager):
...
def create_or_get_order(self, product):
created = None
obj = None
qs = self.get_queryset().filter(product=product, active=True, status='created')
if qs.count() == 1:
obj = qs.first()
else:
# -------------- catch the returned obj and return --------------
obj = self.model.objects.create(product=product)
created = True
return obj, created