Django: UUID type in {% url } tag

Question

Intro

I am following the Django tutorial. In contrast to it I have two databases - MySql and Cassandra. Therefore, I need to use also the Cassandra models which contain the UUID types. Thee UUID has the form of 32 alphanumeric characters and four hyphens (8-4-4-12). Therefore, I have quite complicated regex in my urls.py:

^([A-Fa-f0-9]{8}))(-[A-Fa-f0-9]{4}){3}-[A-Fa-f0-9]{12}

Problem

In the polls/templates/polls/detail.html teplate is the following line:

<form action="{% url 'polls:vote' question.question_id %}" method="post">

The UUID type of question.question_id is then translated to the:

/polls/UUID('47de663a-57f2-4ca1-9ad9-81df9ae25973')/

instead of

/polls/47de663a-57f2-4ca1-9ad9-81df9ae25973/

Therefore, I've got the error message:

Reverse for 'vote' with arguments '(UUID('47de663a-57f2-4ca1-9ad9-81df9ae25973'),)' and keyword arguments '{}' not found. 1 pattern(s) tried:[u'polls/(?P^([A-Fa-f0-9]{8})(-[A-Fa-f0-9]{4}){3}-[A-Fa-f0-9]{12})/vote/$'

Question

How to handle the UUID type?

I suppose I can not use the str(question.question_id) function in the {% url} tag.

Source

Root urls - mysite/urls.py:

from django.conf.urls import url

from . import views

app_name= 'polls'
urlpatterns = [
    #ex: /polls/
    url(r'^$',views.index, name='index'),
    #ex: /polls/uuid
    url(r'^(?P<question_id>^([A-Fa-f0-9]{8})(-[A-Fa-f0-9]{4}){3}-[A-Fa-f0-9]{12})/$', views.detail, name='detail'),
    #ex: /polls/uuid/results/
    url(r'^(?P<question_id>^([A-Fa-f0-9]{8})(-[A-Fa-f0-9]{4}){3}-[A-Fa-f0-9]{12})/results/$', views.results, name='results'),
    #ex: /polls/uuid/vote
    url(r'^(?P<question_id>^([A-Fa-f0-9]{8})(-[A-Fa-f0-9]{4}){3}-[A-Fa-f0-9]{12})/vote/$', views.vote, name='vote'),
]

Polls app polls/urls.py:

from django.conf.urls import url
from . import views

app_name= 'polls'
urlpatterns = [
    url(r'^$',views.index, name='index'),
    #ex: polls/5/results/
    url(r'^(?P<question_id>[0-9]+)/results/$', views.results, name='results'),
    #ex: /polls/5/volte
    url(r'^(?P<question_id>(^([A-Fa-f0-9]{8}))(-[A-Fa-f0-9]{4}){3}-[A-Fa-f0-9]{12})/vote/$', views.vote, name='vote'),
    #ex: polls/5/
    url(r'^(?P<question_id>[^/]+)/$',views.detail, name='detail'),
]

polls/views.py:

from django.shortcuts import render

# Create your views here.

from django.shortcuts import render, get_object_or_404
from .models import Question, Choice
from django.shortcuts import get_object_or_404, render


def index(request):
   #latest_question_list = Question.objects.order_by('-pub_date')[5:]
   latest_question_list = Question.objects()
   context = {
       'latest_question_list': latest_question_list,
   }
   return render(request, 'polls/index.html', context)


def detail(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/detail.html', {'question':question})


def vote(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    try:
        selected_choice = get_object_or_404(Choice, pk=question_id)
        #selected_choice = question.choice_set.get(pk=request.POST['choice'])
    except (KeyError, Choice.DoesNotExist):
        # Redisplay the question voting form.
        return render(request, 'polls/detail.html', {
            'question': question,
            'error_message': "You didn't select a choice.",
        })
    else:
        selected_choice.votes += 1
        selected_choice.save()
        # Always return an HttpResponseRedirect after successfully dealing
        # with POST data. This prevents data from being posted twice if a
        # user hits the Back button.
        return HttpResponseRedirect(
            reverse('polls:results', args=(question.question_id,))
        )

def results(request, question_id):
    question = get_object_or_404(Question, pk=question_id)
    return render(request, 'polls/results.html', {'question': question})

polls/templates/polls/detail.html:

<h1>{{ question.question_text }}</h1>

{% if error_message %}<p><strong>{{ error_message }}</strong></p>{% endif %}

<form action="{% url 'polls:vote' question.question_id %}" method="post">
    {% csrf_token %}
    {% for choice in question.choice_set.all %}
        <input type="radio" name="choice" id="choice{{ forloop.counter }}" value="{{ choice.id }}" />
        <label for="choice{{ forloop.counter }}">{{ choice.choice_text }}</label><br />
    {% endfor %}
    <input type="submit" value="Vote" />
</form>  

polls/Models.py:

from django.db import models

# Create your models here

import uuid
from cassandra.cqlengine import columns
from cassandra.cqlengine import models


from django_cassandra_engine.models import DjangoCassandraModel

class User(models.Model):
    username = columns.Text(primary_key=True)
    password = columns.Text()
    email = columns.Text()
    fullname = columns.Text()
    is_staff = columns.Boolean(default=False)

class ExampleModel(DjangoCassandraModel):
    example_id    = columns.UUID(primary_key=True, default=uuid.uuid4)
    example_type  = columns.Integer(index=True)
    created_at    = columns.DateTime()
    description   = columns.Text(required=False)

class Question(DjangoCassandraModel):
    def __str__(self):
        return self.question_text
    question_id = columns.UUID(primary_key=True)
    question_text = columns.Text()
    pub_date = columns.TimeUUID()

class Choice(DjangoCassandraModel):
    def __str__(self):
        return self.choise_text
    question =  columns.UUID(primary_key=True)
    choice_text = columns.Text()
    votes = columns.Integer(index=True,default=0)

Answer 1

Your question_id regex is wrong. If you're using uuid4 as you appear to be (and assuming you don't want capitals to validate because python's uuid.uuid4() produces lowercase when rendered as a string), the regex for the question_id captured group is:

(?P<question_id>[a-f0-9]{8}-?[a-f0-9]{4}-?4[a-f0-9]{3}-?[89ab][a-f0-9]{3}-?[a-f0-9]{12})

Edit for Django 2.0: Django now has path converters, so you don't need the uuid4 regex anymore. Here's an example:

from django.urls import path

urlpatterns = [
    path('questions/<uuid:question_id>/', MyView.as_view()), 
]