On 10 November 2010 21:55, Shawn Milochik <sh...@milochik.com> wrote:
> The queryset returns zero or more instances of your model. So if
> there's only one result, you can just get the first item in the
> queryset by its index.
>
> For example:
>
> some_queryset = YourModel.objects.filter(**kwargs)
>
> if some_queryset.count() == 1:
> x = some_queryset[0]
> #x is now an instance of your model.
> else:
> raise ValueError("%d results -- expected one!" % (some_queryset.count(),)
This is a very bad way of checking queryset length, because count()
actually creates a new QuerySet that gets executed (again!). Instead
use len() that will first check against queryset's internal cache. In
this special case of one element you can also write:
try:
elem = YourModel.objects.get(**params)
except YourModel.DoesNotExists as e:
# element was not found - do something with it
pass
except YourModel.MultipleObjectsReturned as e:
# there was more then one object that matches given params - if
params include a (primary) key this shouldn't happen
pass
--
Łukasz Rekucki
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