Thats what i was looking for , thanks guys .
On Jun 6, 6:10 pm, Andrew Fong <fongand...@gmail.com> wrote:
> What you're dealing with is called a "race condition". Transactions
> ensure that a set of database operations occur together in a single
> uninterrupted unit. That's not quite the exact definition, but if
> you're picky, see this:http://en.wikipedia.org/wiki/Database_transaction
>
> You can find documentation of Django's support for transactions
> here:http://docs.djangoproject.com/en/dev/topics/db/transactions/
>
> Note that this is dependent on your database supporting transactions.
> If whatever reason your DB doesn't (e.g. using MySQL's MyISAM tables),
> I think using Django's update call will work. Calling
> MyModel.objects.filter(value=10, id=my_id).update(value=15) will
> update the record with the given id to have a value of 15 if and only
> if it's current value is already 10. It returns the number of records
> it successfully modifies, so if there was no conflict, it'll return 1.
> If it returns 0, you know that another process changed the value first
> and that you'll need to get the new value to increment from the
> database again.
>
> -- Andrew
>
> On Jun 6, 10:26 am, Masklinn <maskl...@masklinn.net> wrote:
>
> > On 6 juin 09, at 15:34, AlexM <alex.marge...@gmail.com> wrote:
>
> > > In one of my views i am using a custom manager , the custom manager
> > > finds a user , alters his "balance" (where balance is an integer
> > > value) , and then saves the user with the new balance.
>
> > > The problem occurs when http requests coming really fast on that
> > > view.
>
> > > Lets say the "original" value of a users balance is 10 .
> > > Two requests are made , each one asking for the users balance to be
> > > credited plus 5 of the original one.
> > > The "perfect" solution would be the first requests to be
> > > processed ,saved and then the second to do the same.
>
> > > However what happens is that the first request will come , it will do
> > > its query and load the object , and the second request will also do
> > > the query before the first request was able to complete the process of
> > > saving the new balance, because of that the second request will have
> > > and "out of date" balance which it will then save . So in the end the
> > > user will have 10 (origina ballance) + 5 (second request) = 15 on his
> > > balance when he should have 20.
>
> > > What could i do to prevent this from happening ?
>
> > Use transactions?
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