Bug with prefetch_related

[Uninen]

Posted this few weeks ago to the mailinglist, but seems that it's dead so re-posting here. (Maybe it would be a good idea to retire the mailinglist or post a notification there that it's not been actively followed?)

So, I have a following model with tags:

tags = TaggableManager(through='knuckles.UUIDTaggedItem', blank=True)

where UUIDTaggedItem is:

class UUIDTaggedItem(GenericUUIDTaggedItemBase, TaggedItemBase):

    class Meta:
        verbose_name = "Tag"
        verbose_name_plural = "Tags"

When I query for the tags I get following:

In [18]: e = LiveEvent.objects.get(slug='dj-tony-004')
In [19]: e.tags.all()

Out[19]: <QuerySet [<Tag: 90s>, <Tag: dj tony>, <Tag: house>, <Tag: radioshow>, <Tag: 00's>, <Tag: trance>, <Tag: 90's>, <Tag: eurodance>]>


In [20]: e = LiveEvent.objects.prefetch_related('tags').get(slug='dj-tony-004')
In [21]: e.tags.all()

Out[21]: <QuerySet []>

So when using prefetch_related, I always get empty tags. Not sure if I'm doing something wrong here or if this is a bug?

I'm using Django version 1.11 and django-taggit version 0.22.1

[imhmdb]

I can confirm that this bug still exists almost 4 years after posting the issue, I ended up creating my own tags implementation because prefetching was very important for my use-case, I published a gist explaining how I solved my issue so i'll post it here to help anyone who might stumble upon it while facing the same issue.

https://gist.github.com/imhmdb/af57c9fc4db69bfdfdb900810744e678

[ghost]

This occurs because instance_attr value isn't match _prefetch_related_val.
It worked fine by modifying as below. (only MySQL, SQLite3)

django-taggit/taggit/managers.py

Line 114 in 954d836

return (

            if issubclass(self.through, GenericUUIDTaggedItemBase):
                instance_attr = lambda obj: obj._get_pk_val().hex
            else:
                instance_attr = lambda obj: obj._get_pk_val()

            return (
                qs,
                attrgetter("_prefetch_related_val"),
                instance_attr,
                False,
                self.prefetch_cache_name,
                False,
            )

[jdufresne]

Thanks for looking into this. A PR that contains a test is welcome and will be reviewed.

[Uninen]

Thanks a lot for the patch and the tests, @fumuumuf ! 👍

[Uninen]

This is now fixed with #646

Thank You everyone for your work, waited almost 3 years for this :)