Re: Prefetch object (django 1.7)

[Marcin Szamotulski]

On 01:42 Mon 27 Jan , Marcin Szamotulski wrote:
> Hello,
>
> I have a model
>
> class Post(models.Model):
>
> ...
> authors = models.ManyToManyField('accounts.User', through='PostAuthor', related_name='authors_posts')
>
>
> class PostAuthor(models.Model):
>
> user = models.ForeignKey('accounts.User')
> post = models.ForeignKey(Post)
> ...
>
>
> How can I use the Django 1.7 Prefetch object to load PostAuthors, this
> does not work:
>
> Post.objects.prefetch_related(
> Prefetch(
> 'authors',
> queryset=PostAuthors.object.select_related('user')
> )
>
> I got an exception:
> django.core.exceptions.FieldError: Cannot resolve keyword 'authors_posts' into field. Choices are: created, id, post, post_id,
> user, user_id
>
> Thanks for help,
> Marcin Szamotulski


If somebody will search here is the solution I've found:

Post.objects.prefetch_related(
Prefetch(
'authors',
queryset=User.objects.order_by('postauthor__created'),
)

It works because when prefetching User table is joined (inner joined)
with PostAuthor table and then the order_by('postauthor__created') will
make sense since PostAuthor has a columnt 'created'.

It would be nice to have an example in the docs for that though.

Best regards,
Marcin