Re: Iteration over queryset in a model

On Monday, 10 October 2011 19:14:51 UTC+1, eyscooby wrote:

On Oct 5, 3:11 am, Daniel Roseman <dan...@roseman.org.uk> wrote:
> On Wednesday, 5 October 2011 01:27:54 UTC+1, eyscooby wrote:
>
> > new to django/python developement, can't get this one figured out.
>
> > I have a model that has a couple DateFields (issued_date &
> > completion_date), and I'm trying to return a value with the difference
> > of the two on each entry that is complete, and then if it isn't
> > completed yet, show the amount of days since it was issued.
> > I am using the Admin interface and what I have in the model is
> > this....
>
> > models.py
> > class RequestTicket(models.Model):
> > . . .
> > issued_date = DateField()
> > completed_date = DateField(blank=True, null=True)
>
> > def days_old(self):
> > complete = RequestTicket.object.filter(completion_date__isnull=False)
> > for ticket in complete:
> > return ticket.completion_date - ticket.issued_date
> > return date.today() - self.issued.date
> > days_old.short_discription = 'Days Old'
>
> > what i get returned is if the first entry was completed within 2 days
> > (issued=9/14, completed=9/16), all entries after that get 2 days, even
> > if there is no completion date.
> > If i use 'self.object.filter(completion_date__isnull=False)', I get a
> > NONE answer on all entries
> > If I don't filter for just completed entries I get an error trying to
> > subtract NoneType field with DateField, i guess that might be from the
> > NULL setting.
> > Any help, advice would be great, or if i need to post in another area.
>
> > Django version 1.2
>
> > thanks
> > Kenney
>
> OK, there are a few things wrong with your `days_old` function.
>
> Firstly, it operates on a queryset, not an instance, so it should be a
> method of the Manager, not the Model.  
>
> Secondly, you can't return multiple times like that. You can only return
> once from a function. You need to build up a list of values, and return that
> - or set the attribute on each element of the queryset.
> --
> DR.- Hide quoted text -
>
> - Show quoted text -

DR.
would creating a manager something like this work with a list??

class RequestTicketManager(models.Manager):
def datecalc(self):
complete_list =
list(self.objects.filter(competion_date__isnull=False))
for day in complete_list:
return day.competion_date - day.issued_date

I then put "objects = RequestTicketManager()" in my model

thanks for you help,

You're almost there, but you're still trying to return multiple times. The last few lines should be:

    for day in complete_list:

        day.days_old = day.completion_date - day.issued_date

    return complete_list

Actually, since that calculation is fairly trivial, you could probably do it as an instance method on the model class:

    class RequestTicket(models.Model):

        ...

        def days_old(self):

            return self.completion_date - self.issued_date

The difference between this and the method you first proposed is that this only acts on a single instance at a time - so you'll need to get the queryset of completed items in your view in the normal way, then when you iterate through in the template you can just do {{ ticket.days_old }}.

--

DR.

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