title: Django |add: on PK URL tag
body: <p>I am trying to get the next PK value using |add:"1" in the HTML template. 
  My question is how do I get it to work? Example if PK is 1 it should be 2 after clicking the link. See code.</p>
  
  <p>template</p>
  
  <pre><code> &lt;h3&gt;
      &lt;a href="{% url 'step' task_pk=step.task.pk step_pk=step_id|add:"1" %}"&gt;Next Step&lt;/a&gt;
  &lt;/h3&gt;
  </code></pre>
  
  <p>models</p>
  
  <pre><code>class Task(models.Model):
  CATEGORIES = (
      ('tr', 'Traffic'),
      ('cr', 'Conversion Rate'),
      ('br', 'Bounce Rate'),
      ('ma', 'Marketing'),
      ('sc', 'Sales Channels'),
      ('cur', 'Customer Relations'),
  )
  title = models.CharField(max_length=100)
  description = models.CharField(max_length=300)
  category = models.CharField(max_length=100, choices=CATEGORIES)
  created_at = models.DateTimeField(auto_now_add=True)
  order = models.IntegerField(default=0)
  id = models.AutoField(primary_key=True)
  
  def __str__(self):
      return self.title
  
  
  class Step(models.Model):
  task = models.ForeignKey(Task, on_delete=models.CASCADE)
  order = models.PositiveIntegerField(default=1)
  title = models.CharField(max_length=100)
  is_complete = models.BooleanField(default=False)
  description = models.TextField()
  id = models.AutoField(primary_key=True)
  
  class Meta:
      ordering = ['order']
      unique_together = ("task", "order")
  
  def __str__(self):
      return self.title
  </code></pre>
  
  <p>views</p>
  
  <pre><code>def task_step(request, task_pk, step_pk):
  step = get_object_or_404(Step, task_id=task_pk, pk=step_pk)
  return render(request, 'totd/task_step.html', {'step': step})
  </code></pre>
  
  <p>urls</p>
  
  <pre><code>urlpatterns = [
  re_path(r'(?P&lt;task_pk&gt;\d+)/(?P&lt;step_pk&gt;\d+)/$', views.task_step, name='step'),
  ]
  </code></pre>