Perhaps you could supply more information regarding your models and what you are trying to achieve. Something like this might help:
models.py
class Article(models.Model):
category = models.ForeignKey(Category, related_name='article')
...
Where ever you return a queryset in views:
def get_context_data(self, **kwargs):
context = super(ArticleView, self).get_context_data(**kwargs)
context['articles'] = Article.objects.all().select_related('category')
return context
In templates:
{% for article in articles %}
{% for category in article.category %}
{{ category.get_absolute_url }}/{{ category.slug }} # this will return a string: abs_url/slug
{% endfor %}
{% endfor %}
Read about select_related here: https://docs.djangoproject.com/en/dev/ref/models/querysets/#select-related
You could also take a look at implementing Managers: https://docs.djangoproject.com/en/dev/topics/db/managers/#django.db.models.Manager