django template internal url concatenation - django

Question

In my django project, I have URL patterns like below.
urls.py in project root:
urlpatterns = [
path('', include('blog.urls')),
]
urls.py in app(blog) root:
urlpatterns = [
path('', views.index, name='index'),
path(
'category/<str:category_id>',
views.category_view,
name='category_view',
),
]
What I want to do is making hyperlink for each category with django template. Something like below.
{% for category in categories %} .
<a href="{{ {% url 'index' %}|add: {% url 'category_view' category %} }} " class="nav">
{{category}}
</a>
{% endfor %}
However, it doesn't work. There are too many categories that I can't hard code any of them, but have to make url "(domain root)/category/(category name)" with django template. How can I concatinate two url in a template (as django does with
path(A, include(B))
)

Answer 1

You can define a get_absolute_url method in your Category model, it is a much cleaner solution: https://docs.djangoproject.com/en/2.1/ref/models/instances/#get-absolute-url
Implementation example:
from django.urls import reverse_lazy
# for django < 1.10 from django.core.urlresolvers import reverse_lazy
class Category(models.Model):
...
def get_absolute_url(self):
return reverse_lazy('category_view', category_id=self.id)
and in your template:
{% for category in categories %} .
<a href="{{ category.get_absolute_url }}" class="nav">
{{category}}
</a>
{% endfor %}