I am using transaction, but still have the problem. ;( You are right, my problem is from "concurrent requests", which I have searched in this group, but haven't found a very good solution...
On 7月2日, 上午1时45分, phillc <[EMAIL PROTECTED]> wrote: > i think you need transactions? > > problem being that if all those processes happen at about the same > time, they will all see enough money, then they will all process it. > > On Jul 1, 5:12 am, pength <[EMAIL PROTECTED]> wrote: > > > > > 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!- 隐藏被引用文字 - > > - 显示引用的文字 - --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Django users" group. To post to this group, send email to django-users@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/django-users?hl=en -~----------~----~----~----~------~----~------~--~---
