[BangPypers] BangPypers Digest, Vol 83, Issue 3

[Pratik Mandrekar]

Notes on using the post_save signal

1 - Do not use post_save to save the instance that is passed. The
`instance.save` is going to cause a never ending loop.
2 - Use post_save signal to do  things not related to updating the model
being saved. Like updating a related model.
3 - Override the save method of the model to do any changes you need to do
to override the default save.
4 - If you have to use signals in this case (Eg. You cannot edit the models
because they are part of a different library) use the pre_save signal and
just modify the attributes without calling `instance.save()`


On Tue, Jul 8, 2014 at 3:30 PM, <bangpypers-request at python.org> wrote:

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> Today's Topics:
>
>    1. Anyone Travelling for EuroPython ? (konark modi)
>    2. Django - Infinte Loop (Anand Reddy Pandikunta)
>    3. Re: Django - Infinte Loop (kracekumar ramaraju)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 7 Jul 2014 21:49:07 +0530
> From: konark modi <modi.konark at gmail.com>
> To: Bangalore Python Users Group - India <bangpypers at python.org>
> Subject: [BangPypers] Anyone Travelling for EuroPython ?
> Message-ID:
>         <
> CAPhs5j_9hrF-JAvT+uhbCA8HfxaOjk8sYrzL__UXaA04Q7YE1g at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> Hi
>
> Wanted to know if anyone on the list is planning to travel for EuroPython
> 2014 this July.
>
> Regards
> Konark
>
>
> ------------------------------
>
> Message: 2
> Date: Tue, 8 Jul 2014 13:13:02 +0530
> From: Anand Reddy Pandikunta <anand21nanda at gmail.com>
> To: Bangalore Python Users Group - India <bangpypers at python.org>
> Subject: [BangPypers] Django - Infinte Loop
> Message-ID:
>         <CALCtiO56Lk=yB7003L20aku9UXn8b_FAUQcrdo=
> nHOFnLVqniQ at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
>
> Hi,
>
> *models.py*
>
> *def my_func(sender, instance, created, **kwargs):*
> *      # do something*
> *      instance.status = 'task completed'*
> *      instance.save()*
>
> *class MyModel(models.Model):*
> *      status = models.CharField(max_length=100, blank=True)*
> *      # some code*
>
> *signals.post_save.connect(my_func, sender=MyModel)*
>
>
> I am using post_save signal to connect to a function.
>
> If a new instance of model is saved, post_save signal connects to my_func.
> Once the function is executed, I am updating status of the model.
> This is again sending post_save signal which is leading to infinite loop.
>
> I want to execute my_func only once and update status many times.
> Does any one know how to do this?
>
>
> --
> - Anand Reddy Pandikunta
> www.avilpage.com
> www.quotes160.com
>
>
> ------------------------------
>
> Message: 3
> Date: Tue, 8 Jul 2014 13:27:09 +0530
> From: kracekumar ramaraju <kracethekingmaker at gmail.com>
> To: Bangalore Python Users Group - India <bangpypers at python.org>
> Subject: Re: [BangPypers] Django - Infinte Loop
> Message-ID:
>         <CAO5c=mk0v9nyGRVdtVfhTz68=PLfNnif7nKdh=
> u96wVFwP6DEQ at mail.gmail.com>
> Content-Type: text/plain; charset=UTF-8
>
> Hi Anand
>
>  I would save *don't* use Django signal. Signals are hard to test and don't
> know when they will be executed.
>
> Suggestions
> - If post_save function does some work like updating external service which
> can take data, use rq or celery.
> - You can override django save.
>
> class MyModel(BaseClass):
>
>     def save(self, **kwargs)
>        # set all attributes
>       # call super class save
>       # call function here - blocking call.
>
>
>
>
>
> On Tue, Jul 8, 2014 at 1:13 PM, Anand Reddy Pandikunta <
> anand21nanda at gmail.com> wrote:
>
> > Hi,
> >
> > *models.py*
> >
> > *def my_func(sender, instance, created, **kwargs):*
> > *      # do something*
> > *      instance.status = 'task completed'*
> > *      instance.save()*
> >
> > *class MyModel(models.Model):*
> > *      status = models.CharField(max_length=100, blank=True)*
> > *      # some code*
> >
> > *signals.post_save.connect(my_func, sender=MyModel)*
> >
> >
> > I am using post_save signal to connect to a function.
> >
> > If a new instance of model is saved, post_save signal connects to
> my_func.
> > Once the function is executed, I am updating status of the model.
> > This is again sending post_save signal which is leading to infinite loop.
> >
> > I want to execute my_func only once and update status many times.
> > Does any one know how to do this?
> >
> >
> > --
> > - Anand Reddy Pandikunta
> > www.avilpage.com
> > www.quotes160.com
> > _______________________________________________
> > BangPypers mailing list
> > BangPypers at python.org
> > https://mail.python.org/mailman/listinfo/bangpypers
> >
>
>
>
> --
>
> *Thanks & Regardskracekumar"Talk is cheap, show me the code" -- Linus
> Torvaldshttp://kracekumar.com <http://kracekumar.com>*
>
>
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> ------------------------------
>
> End of BangPypers Digest, Vol 83, Issue 3
> *****************************************
>