Question

I have a queryset containing some objects. Depending on some case or the other i now want to exclude all the objects without certain tags (_tags is the name of the TagField on my model):

self.queryset=self.queryset.exclude(_tags__id__in=avoid)

But this just leaves me with an error:

Caught FieldError while rendering:
Join on field '_tags' not permitted.
Did you misspell 'id' for the lookup type?

As i’m pretty sure i did not misspell ‘id’, i did some searching on how to use tagging for something like this. In the docs there is a lot about custom Managers, but somehow i just can’t get it how i can use them to get what i want.

edit:

corrected the code above to

self.queryset=self.queryset.exclude(_tags__in=avoid)

where avoid is a list of integers. And that leaves me with the problem that the TagField of django-tagging is just a special CharField (or TextField?). Which will, of course, not sort out anything if i just query it against a list of integers. I could try to solve this in a way like this:

for tag in avoid:
    self.queryset=self.queryset.exclude(_tags__contains=tag.name)

which is not only ugly, but also leaves me with the problem of tags made of multiple words or matching parts of other tags.

I somehow have the suspicion that this could be solved in a much prettier way by someone who has understood how django-tagging works.

Answer 1

As described in the comment on Chris’ answer, django-tagging does not deliver the tagstring when accessing model._tag. In the end i had no other solution than to do the query and sort out the loops containing a certain tag afterwards:

itemlist = list(queryset)
avoid = some_list_of_tag_ids            
# search for loops that have NONE of the avoid tags
for item in itemlist:
    #    has tags   and [ if a tag.id in avoid this list has an element]
    if (item.tags)  and [tag for tag in item.tags if tag.id in avoid]:
        # remove the item from the list
        itemlist.remove(item)

To complete that the model for this looks like this:

class Item(models.Model):

    _tags = TagField(blank=True,null=True)

    def _get_tags(self):
        return Tag.objects.get_for_object(self)
    def _set_tags(self, tags):
        Tag.objects.update_tags(tags)

    tags = property(_get_tags, _set_tags)

Allthough i tried for quite a while, i found no way of chaining a query against tagging tags into a query chain for an object. For this project I’m stuck with tagging, but this is a real drawback…