title: Getting error no such column: blog_comment.url, despite making migrations
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>Originally I thought the problem was because I had not included a slug field in my class called Comments. Then I added <code>url= models.SlugField(max_length=500, unique=True, blank=True)</code>. Do I now need to reset the database linked to this class? If so how do I achieve that? Or am I going off at a massively incorrect tangent? </p>
  
  <p><a href="https://i.stack.imgur.com/3aVBA.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/3aVBA.png" alt="enter image description here"></a>
  <a href="https://i.stack.imgur.com/9Z82i.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9Z82i.png" alt="enter image description here"></a></p>
  
  <p><strong>models.py</strong></p>
  
  <pre><code>from django.db import models
  from django.utils.text import slugify
  from django.utils import timezone
  from django.contrib.auth.models import User
  from django.urls import reverse
  
  
  # 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)
      url= models.SlugField(max_length=500, unique=True, blank=True)
  
      class Meta:
          ordering = ['created_on']
  
      def __str__(self):
          return 'Comment {} by {}'.format(self.body, self.name)
  
      def save(self, *args, **kwargs):
          self.url= slugify(self.post)
          super().save(*args, **kwargs)
  
      def get_absolute_url(self):
          return reverse('article_detail', kwargs={'slug': self.slug})
  </code></pre>
  
  <p><strong>views.py</strong></p>
  
  <pre><code>def post_detail(request, pk):
  template_name = 'post_detail.html'
  
  comments = Comment.objects.filter(post=pk ,active=True)
  post = Post.objects.get(pk=pk)
  new_comment = None
  # Comment posted
  if request.method == 'POST':
      comment_form = CommentForm(data=request.POST)
      if comment_form.is_valid():
  
          # Create Comment object but don't save to database yet
          new_comment = comment_form.save(commit=False)
          # Assign the current post to the comment
          new_comment.post = post
          # Save the comment to the database
          new_comment.save()
  else:
      comment_form = CommentForm()
  
  return render(request, template_name, {'post': post,
                                         'comments': comments,
                                         'new_comment': new_comment,
                                         'comment_form': comment_form})
  </code></pre>
  
  <p><strong>Migrations</strong></p>
  
  <p>I have now made (or attempted to make) the necessary migrations.</p>
  
  <pre><code>WARNINGS:
  ?: (2_0.W001) Your URL pattern '^activate/(?P&lt;uidb64&gt;[0-9A-Za-z_\-]+)/(?P&lt;token&gt;[0-9A-Za-z]{1,13}-[0-9A-Za-z]{1,20})/$' [name='activate'] has a route that contains '(?P&lt;', begins with a '^', or ends with a '$'. This was likely an oversight when migrating to django.urls.path().
  blog.Post.date_posted: (fields.W161) Fixed default value provided.
          HINT: It seems you set a fixed date / time / datetime value as default for this field. This may not be what you want. If you want to have the current date as default, use `django.utils.timezone.now`
  Migrations for 'blog':
    blog\migrations\0014_auto_20200420_2034.py
      - Add field url to comment
      - Alter field date_posted on post
  
  
  # Generated by Django 2.2.6 on 2020-04-20 13:34
  
  import datetime
  from django.db import migrations, models
  from django.utils.timezone import utc
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('blog', '0013_auto_20200410_0107'),
      ]
  
      operations = [
          migrations.AddField(
              model_name='comment',
              name='url',
              field=models.SlugField(blank=True, max_length=500, unique=True),
          ),
          migrations.AlterField(
              model_name='post',
              name='date_posted',
              field=models.DateTimeField(default=datetime.datetime(2020, 4, 20, 13, 34, 51, 980840, tzinfo=utc)),
          ),
      ]
  </code></pre>