old_contents: from django.contrib.auth.models import User
  from django.db import models
  
  
  # Create your models here.
  class Article(models.Model):
      user = models.ForeignKey(User)
      content = models.CharField('text')
  
new_contents: from django.contrib.auth.models import User
  from django.db import models
  
  
  # Create your models here.
  class Article(models.Model):
      user = models.ForeignKey(User)
      content = models.CharField('text', max_length=100)
  
subject: Fix demo models.