title: name 'slugify' is not defined
body: <p>Once a user had logged into my site he could write a post and update it. </p>
  
  <p>Then I was making progress in adding functionality which allowed people to make comments. I was at the stage where I could add comments from the back end and they would be accurately displayed on the front end. </p>
  
  <p>Now when I try and update posts I get an error message. </p>
  
  <p><a href="https://i.stack.imgur.com/uq5Z8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uq5Z8.png" alt="enter image description here"></a></p>
  
  <p>I assume it is because there is a foreign key linking the comments class to the post class. I tried Googling the problem and looking on StackOverflow but I wasn't entirely convinced the material I was reading was remotely related to my problem. I am struggling to fix the issue because I barely even understand / know what the issue is. </p>
  
  <pre><code>    # Create your models here.
  class Post(models.Model):
      title = models.CharField(max_length=100)
      content =  models.TextField()
      date_posted = models.DateTimeField(default=timezone.now())
      author = models.ForeignKey(User, on_delete=models.CASCADE)
      url= models.SlugField(max_length=500, unique=True, blank=True)
  
  def save(self, *args, **kwargs):
      self.url= slugify(self.title)
      super().save(*args, **kwargs)
  
  def __str__(self):
      return self.title 
  
  def get_absolute_url(self):
      return reverse('article_detail', kwargs={'slug': self.slug})
  
  
  class Comment(models.Model):
      post = models.ForeignKey(Post,on_delete=models.CASCADE,related_name='comments')
      name = models.CharField(max_length=80)
      email = models.EmailField()
      body = models.TextField()
      created_on = models.DateTimeField(auto_now_add=True)
      active = models.BooleanField(default=False)
  
  class Meta:
      ordering = ['created_on']
  
  def __str__(self):
      return 'Comment {} by {}'.format(self.body, self.name)
  </code></pre>