On 12/11/06, jerf <[EMAIL PROTECTED]> wrote:
> Is there a way to "catch" a property change so I can run some code at
> the time?
>
> Example:
>
> --------
> class Entry(models.Model):
> ...
> post_date = models.DateTimeField(...)
> posted = models.BooleanField(...)
>
> e = Entry.create()
> e.save()
> e.posted = True
> --------
>
> I want to be able to run some code on the last line to automatically
> update 'post_date' at that time.
>
> It would also be acceptable to do this in a .save() override, but I
> can't find a (documented/supported) way to access the old value to
> compare it against the new value at that time.
>
> This would cleanly solve several problems for me, many of which are
> more complicated and tricky than this minimal example.
Hi Jerf,
You can simply write a set_posted() method, like so:
class Entry(models.Model):
post_date = models.DateTimeField(...)
posted = models.BooleanField(...)
def set_posted(self, new_value):
if new_value != self.posted:
self.post_date = datetime.datetime.now()
This won't work with the admin interface, because it wouldn't know
about your set_posted() method. With that said, you might be able to
use Python properties, but I have never tried that and am not sure
whether it would work. If it did work, you could do this:
class Entry(models.Model):
post_date = models.DateTimeField(...)
posted = models.BooleanField(...)
def set_posted(self, new_value):
if new_value != self.posted:
self.post_date = datetime.datetime.now()
posted = property(set_posted)
...and any time you set the "posted" attribute, it would call
set_posted() behind the scenes. Like I said, though, I'm not sure
whether that would work with the way models are currently implemented.
(But if not, let's go ahead and fix that!)
Adrian
--
Adrian Holovaty
holovaty.com | djangoproject.com
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