old_contents: from django.db import models
  from django.utils.translation import ugettext as _
  from django.utils.timezone import now
  
  
  try:
      from django.contrib.auth import get_user_model
      User = get_user_model()
  except:
      from django.contrib.auth.models import User
  
  
  class Note(models.Model):
      author = models.ForeignKey(
          User,
          verbose_name=_('author'),
          related_name='notes',
      )
      message = models.CharField(
          _('message'),
          max_length=200,
      )
      posted_at = models.DateTimeField(
          _('publication date'),
      )
  
      def save(self, *args, **kwargs):
          if self.pk is None:
              self.posted_at = now()
          super(Note, self).save(*args, **kwargs)
  
      class Meta:
          verbose_name = _('note')
          verbose_name_plural = _('notes')
          ordering = ('-posted_at', )
  
new_contents: from django.db import models
  from django.utils.translation import ugettext as _
  from django.utils.timezone import now
  
  
  try:
      from django.contrib.auth import get_user_model
      User = get_user_model()
  except:
      from django.contrib.auth.models import User
  
  
  class Note(models.Model):
      author = models.ForeignKey(
          User,
          verbose_name=_('author'),
          related_name='notes',
      )
      message = models.CharField(
          _('message'),
          max_length=200,
      )
      posted_at = models.DateTimeField(
          _('publication date'),
          auto_now_add=True,
      )
  
      class Meta:
          verbose_name = _('note')
          verbose_name_plural = _('notes')
          ordering = ('-posted_at', )
  
subject: Remove save method for auto_now_add=True