How to know if an object is being created in the save() method?

[Julien]

Hello there,

Does the title says it all? When overriding the save method of an
object, I'd like to know if that object is being created or updated.

How I do it so far is:

def save(self):
if self.pk:
...=> being created
else:
...=> being updated

I vaguely remember seeing a parameter for the save method which would
do that, but I can't find it. Any thoughts?

Thanks!

Julien

[Ivan Illarionov]

There is 'post_save' signal with 'created' parameter. But,
unfortunately, this feature is undocumented...

[Eren Türkay]

On 31 Jan 2008 Thu 06:22:43 Ivan Illarionov wrote:
> There is 'post_save' signal with 'created' parameter. But,
> unfortunately, this feature is undocumented...

It's something related with "dispatcher" class? Please let me know if there is
more about signals than the code below. I simply just use this;

-----
...
...
from django.db.models import signals
from django.dispatch import dispatcher
from myapp.signal_handlers import do_something_before_adding

class FooModel(models.Model)
.....
.....

dispatcher.connect(do_something_before_adding, signal=signals.pre_save,
sender=FooModel)

-----

This code will call "do_something_before_adding" before the object is created.
I don't know what parameters are appended to function, but just do triald and
error :) I hope, this will help you Julien.

Btw, in the "django.db.models.signals", these signals exist;

class_prepared
pre_init
pot_init
pre_save
post_save
pre_delete
post_delete
post_syncdb

[Michael Elsdörfer]

>> There is 'post_save' signal with 'created' parameter. But,
>> unfortunately, this feature is undocumented...
>
> It's something related with "dispatcher" class? Please let me know if
> there is more about signals than the code below. I simply just use
> this;

If you use post_save instead of pre_save, your signal handler is passed
a 'created' flag.

Michael

[Michael Elsdörfer]

> def save(self): if self.pk: ...=> being created else: ...=> being
> updated
>
> I vaguely remember seeing a parameter for the save method which would
> do that, but I can't find it. Any thoughts?

That's the correct way to do it, unless you want to use signals:

http://www.martin-geber.com/weblog/2007/10/29/django-signals-vs-custom-save-method/

Michael

[Ivan Illarionov]

Example of post_save with 'created' flag is in Django tests:
http://code.djangoproject.com/browser/django/trunk/tests/modeltests/signals/models.py