On Wed, 2007-03-14 at 20:26 +0000, Norjee wrote:
> Imagine the following model:
>
> class Article(models.Model):
> title = models.IntegerField()
>
> Then when you do case 1):
> art = Article.objects.get(pk=1)
> art.title = "New title"
> art.save()
>
> or case 2):
> art = Article.objects.get(pk=1)
> art.save()
>
> Is there a way that the model, before saving, knows whether the title
> (or any other field) has been reassigned? I need to know because for a
> datefield I want to use now if no explicit date is given, otherwise
> the given date.
There's no one-line method, but it's pretty easy to do: write a custom
save() method on the Article class that retrieves the instance again and
compares the fields. Something like
def save(self):
if self.id:
original = Article.objects.get(id=self.id)
# Compare fields you care about
super(Article, self).save()
The reason this can't really be done any more simply than that is that
the attributes on an Article instance are just normal Python attributes
-- there is nothing Field-like about them until you do the saving.
Python has no automatic way to tell if a class's attributes have changed
between two points in time.
Reagrds,
Malcolm
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