I have a problem in one of my models. I'm uploading an image, and I want to store the id (pk in the database table) but I need to know at which point Django will have access to self.id.

models.py

class BicycleAdItemKind(MPTTModel):
    def url(self, filename):
        pdb.set_trace()

        url = "MultimediaData/HelpAdImages/ItemKind/%s/%s" % (self.id, filename)
        return url

    def item_kind_image(self):
        return '<img align="middle" src="/media/%s" height="60px" />' % self.image
    item_kind_image.allow_tags = True     

    # Bicicleta completa, Componentes para bicicleta, Acessorios para ciclista
    n_item_kind      = models.CharField(max_length=50) 
    parent           = TreeForeignKey('self', null=True,
                                      blank=True, related_name='children')
    description      = models.TextField(null=True, blank=True)
    image            = models.ImageField(upload_to=url, null=True, blank=True)
    date_inserted    = models.DateTimeField(auto_now_add=True)
    date_last_update = models.DateTimeField(auto_now=True)

    def __unicode__(self):
        return self.n_item_kind

    class MPTTMeta:
        order_insertion_by = ['n_item_kind']

The problem is in the url() method; I can only get self.id when updating an object, I don't get the self.id when creating a new object. How can I modify this model so that I get self.id when creating a new object?

With the current code, when I'm creating a new object I will end up with a url like:

MultimediaData/HelpAdImages/ItemKind/None/somefile.jpg

And I need to have something like:

MultimediaData/HelpAdImages/ItemKind/35/somefile.jpg

Any clues?

django django-models django-mptt
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