On Sat, 2009-04-25 at 04:37 -0700, medhat wrote:
> Here is a small example:
>
> class Item(models.Model):
> title = models.CharField(max_length=25)
> other = models.TextField(null=True, blank=True)
> items = models.ManyToManyField('self', null=True, blank=True)
>
> def __unicode__(self):
> return self.title
>
> def save(self, force_insert=False, force_update=False):
> super(Item, self).save(force_insert, force_update)
> if self.other.strip():
> pieces = [x.strip() for x in self.other.split(',')]
> self.items.clear()
> for piece in pieces:
> other = Item.objects.get(title=piece)
> self.items.add(other)
>
> the idea here is that the user can specify the items in the
> ManyToManyField by providing a comma-separated list of item titles in
> the "other" field. This works fine from shell. It does not work from
> the admin site, I think because the form saves related data *after*
> the model itself is saved, so my code in save() runs, but it seems
> that after that it gets overwritten by the form.
>
> So, what is the best way to do what I am trying to do? I am hoping to
> be able to do it in the model (since that's where I think it belongs)
Trying to do this at the model level is always going to be fragile. If
you want to store this as a many-to-many field at the model level, then
only have the ManyToManyField. The "other" field you have is trying to
work around the problem.
Okay, so you want people to be able to supply a comma-separated list of
values in a form. So do that at the form level and don't dirty your
model with the details. Programmers populating the model can do things
the direct way and supply the many related objects -- the programmatic
API for that is very easy to use. It should only be the form case that
you need to worry about.
Regards,
Malcolm
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