sorry for the bad indent of the "#models.py" part. I post it again,
hope this time that part will be shown OK.
#models.py
class Apple_For_Sale(models.Model):
price = models.PositiveSmallIntegerField()
has_been_sold = models.BooleanField(default=False)
class People(models.Model):
money = models.PositiveSmallIntegerField()
def buy_apple(self,apple): #apple should be an instance of
Apple_For_Sale
if self.money >= apple.price and not apple.has_been_sold:
self.money -= apple.price
self.save()
apple.has_been_sold = True
apple.save()
Sale_Records.objects.create(apple=apple,people=self)
class Sale_Records(models.Model): #create one record when one people
buy
apple = models.ForeignKey(Apple_For_Sale)
people = models.ForeignKey(People)
dealt_date = models.DateTimeField(auto_now_add=True)
On Jul 1, 4:53 pm, pength <[EMAIL PROTECTED]> wrote:
> I am using Django0.96/apache2/mod_python(running prefork MPM) / mysql,
> for my Django project, a typical Django environment, I think. And
> usually there're more than 10 apache2 processes running on my site, as
> the online users is about 100+.
>
> I found a problem that sometimes if one user clicks a link several
> times very fast (means several identical requests are sent to the
> server), some error will happen. Although in my codes, I am tring to
> prevent such thing. Let me make a simple example to illustrate my
> problem.
>
> #models.py
> class Apple_For_Sale(models.Model):
> price = models.PositiveSmallIntegerField()
> has_been_sold = models.BooleanField(default=False)
>
> class People(models.Model):
> money = models.PositiveSmallIntegerField()
>
> def buy_apple(self,apple): #apple should be an instance of
> Apple_For_Sale
> if self.money >= apple.price and not apple.has_been_sold:
> self.money -= apple.price
> self.save()
> apple.has_been_sold = True
> apple.save()
>
> Sale_Records.objects.create(apple=apple,people=self)
>
> class Sale_Records(models.Model): #create one record when one people
> buy
> apple = models.ForeignKey(Apple_For_Sale)
> people = models.ForeignKey(People)
> dealt_date = models.DateTimeField(auto_now_add=True)
>
> #views.py
> def people_buy_apple(request,aid):
> "aid is the id of an apple_for_sale
> a = get_object_or_404(Apple_For_Sale, pk=aid)
> p = People.object.get(xxx) #....get people...omitted here
> p.buy_apple(a)
> return ....
>
> The logic is simple. If the people has enough money and the apples
> have not already been sold, then the "buy apple" will be successful.
>
> And in my site, I think 99% of such things happened correctly. But,
> very rarely, when one user clicks a link of "buy apple" several times
> fast, there'll be more than 1 records of Sale_Records created, for
> same "apple" and "people", and the people's money was minused several
> times for one identical apple. And if the network is laggy, it seems
> the frequency of such error occurs becomes higher.
>
> For my understanding, when the several "identical requests" are sent
> to my server, the requests are dispatched to different apache2
> processes, and nearly the same time, each process "think" the "buy
> apple" can happen successfully. so....the error comes out.
>
> In my actual site, I have added some "unqiue = True" to avoid this
> kind of error, in DB level. For example:
> class Sale_Records(models.Model):
> apple = models.ForeignKey(Apple_For_Sale, unique=True)
>
> But really I doubt this is the right way to solve my problem.
>
> Can anyone help? Can I avoid such error by using "mod_wsgi in daemon
> mode with only 1
> thread " (ref. to
> :http://groups.google.com/group/django-users/browse_thread/thread/5bd5...)
>
> Thanks a lot!
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