On Tuesday 23 May 2006 20:04, medhat wrote:
> 1. I would like to generate the 'upload_to' parameter of the
> FileField based on the value of another field in my model.
>
> example:
>
> ===
> class File(models.Model):
> title = models.CharField(maxlength=50)
> project = models.ForeignKey(Project)
> document = models.FileField(upload_to='files/' + self.title +
> '/',blank=True,null=True)
> ===
>
>
> 2. I would like to use some value from my instance to create the Q
> object passed to the 'limit_choices_to' parameter.
>
> example:
>
> ===
> class File(models.Model):
> title = models.CharField(maxlength=50)
> project = models.ForeignKey(Project)
> supercedes =
> models.ForeignKey('self',limit_choices_to=Q(project=self.project,blan
>k=True,null=True) ===
You can't do either of these with Django -- limit_choices_to and
upload_to are defined as attributes of the model, and not instances.
To enable something like this, they would have to be defined as
callables that take a model instance as a parameter, or something like
that.
However, you've still got problems with both your examples. In
particular, when would those callables be called? In your examples,
the behaviour of one field (and associated admin and manipulator
functionality) depends on values of other instance variables, so the
order in which those fields get updated will affect the outcome. Also,
if the user changed the 'project', the admin would have to immediately
do a round trip to the server to update the 'supercedes' options -- how
would it know to do this?
A work-around for the first case is to override save() and move the
document to the correct folder after the model instance has been saved.
Luke
--
"The truth will set your teeth free." (Calvin and Hobbes)
Luke Plant || L.Plant.98 (at) cantab.net || http://lukeplant.me.uk/
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