Django database migrations best practices

                  from django.db import migrations


def populate_slugs(apps, schema_editor):
    """Generate slugs for existing posts."""
    Post = apps.get_model('blog', 'Post')
    from django.utils.text import slugify

    for post in Post.objects.filter(slug__isnull=True):
        post.slug = slugify(post.title)
        post.save()


def reverse_populate_slugs(apps, schema_editor):
    """Clear slugs."""
    Post = apps.get_model('blog', 'Post')
    Post.objects.update(slug=None)


class Migration(migrations.Migration):
    dependencies = [
        ('blog', '0002_post_slug'),
    ]

    operations = [
        migrations.RunPython(populate_slugs, reverse_populate_slugs),
    ]