On 3 avr, 23:12, Adam Tonks <[email protected]> wrote:
> I have a function in a model to return the first post in a forum thread. At
> the moment, it looks like this:
>
> return Post.objects.filter(thread = self.pk).order_by('created')
>
> When I run it in my test forum, the code returns two posts:
>
> [<Post: This post is a test post to display when the...>, <Post: This is a
> reply to the test post.>]
>
> I then add a [0] to the end of the statement, to just return the first item,
> creating this return statement:
>
> return Post.objects.filter(thread = self.pk).order_by('created')[0]
>
> This, however, gives me "Caught IndexError while rendering: list index out of
> range".
>
> The only thing I changed the entire time was adding the [0]. I tested on the
> same forum, with the same data etc.
If you really did test on the very same data set, same forum, *same
thread* (IOW ; same value for "self.pk") etc, you would'nt get an
IndexError, so there's obviously something different.
> If I remove the filter part (making the statement below), it works fine,
> returning the first post in the queryset.
>
> return Post.objects.order_by('created')[0]
This returns all posts, whatever thread they belongs to.
>
> I have no idea why adding the [0] to get the first result of the queryset is
> causing it to return an empty queryset.
It's not "causing it to return an empty queryset", it's raising an
index error because your queryset is already empty.
> If anyone has any suggestions as to what I could do, it'd be much appreciated.
try:
Post.objects.filter(thread = self.pk).order_by('created')[0]
except IndexError:
# just so you know your queryset is really empty
# comment this out (or even better remove it) once you made sure
# the error was in your test, not in Django
if Post.objects.filter(thread = self.pk).count():
raise AssertionError("Something has gone terribly wrong")
# here you may want to either return None if an empty thread is ok
for your,
# or raise some specific exception else
return None
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