old_contents: from django.db import models
  
  
  class Product(models.Model):
  
      name = models.CharField(max_length=150, unique=True)
  
      def __unicode__(self):
          return u'%s' % (self.name, )
  
new_contents: from django.db import models
  
  
  class Product(models.Model):
  
      name = models.CharField(max_length=150, unique=True)
      barcode = models.IntegerField(blank=True, null=True)
  
      def __unicode__(self):
          return u'%s' % (self.name, )
  
subject: add barcode field