Thanks a lot Dan,
It's exactly what I was looking for. It was so easy. Now I can see.
Thanks Again.
On Wed, Sep 30, 2009 at 3:50 PM, Dan Ostrowski <dan.ostrow...@gmail.com>wrote:
>
> Sounds like you need an atomic operation.
>
> Instead of doing a SELECT, do an UPDATE and then check the affected
> rows, such as:
>
> UPDATE table SET flag = 1 WHERE flag = 0;
>
> Then check if the operation succeeded.
>
> Cheers,
> Dan
>
> On Sep 30, 11:38 am, gustavo Cardoso <gnasce...@gmail.com> wrote:
> > Acctually,
> >
> > I need to do a SELECT in a table. In this table has a flag field. if the
> > flag field has 0 so I can update de flag field to 1.
> > In other words I need to do a SELECT by verifing if the flag field is 0.
> And
> > after, I can update to 1 the flag field.
> >
> > But the problem is: More than one access occurr in this table.
> >
> > Imagine A and B (two users) accessing this table.
> > A do a SELECT.
> > B do a SELECT.
> > A verify that the flag field is 0.
> > B verify that the flag field is 0.
> > A UPDATE to 1 the flag field.
> > B UPTADE to 1 the flag field. (Wrong!! B couldn't set the flag to 1
> > because the flag already was configured to 1.)
> >
> > But B must to wait for A. A need to put the flag in 0 again. So B can put
> > the flag in 1 and use the datas.
> >
> > is there a way to resolve this problem in django?? Can put some example?
> >
> > thanks
> >
> > On Wed, Sep 30, 2009 at 10:05 AM, Kristaps Kūlis
> > <kristaps.ku...@gmail.com>wrote:
> >
> >
> >
> >
> >
> > > Create locks and store them at cache as keys.
> > > Or implement counter as cache.incr('users_online')
> >
> > > On Wed, Sep 30, 2009 at 3:52 AM, Nan <ringe...@gmail.com> wrote:
> >
> > >> Any particular reason you can't just use User.objects.count() ?
> >
> > >> On Sep 29, 7:16 pm, gustavo Cardoso <gnasce...@gmail.com> wrote:
> > >> > Hello Folks,
> >
> > >> > I need to implement a Counter.
> > >> > One variable to store the number of users in my site.
> > >> > This variable can't be access in the same time for more than one
> user.
> > >> > How I do this in django. How I create a method that only one user
> can
> > >> access
> > >> > in the same time?
> > >> > Is there some API to lock and release that variable?
> > >> > Thanks!
> >
> > >> > --
> > >> > Gustavo Nascente Cardoso
> > >> > Ciência da Computação - UFES
> >
> > --
> > Gustavo Nascente Cardoso
> > Ciência da Computação - UFES
>
> >
>
--
Gustavo Nascente Cardoso
Ciência da Computação - UFES
--~--~---------~--~----~------------~-------~--~----~
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
django-users+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/django-users?hl=en
-~----------~----~----~----~------~----~------~--~---
