Fixture-friendly DateTimeField w.r.t auto_now, auto_now_add

gistfile1.py

# Fixture-friendly DateTimeField w.r.t auto_now, auto_now_add
# >>> created_at = AutoDateTimeField(auto_now_add=True)
# >>> updated_at = AutoDateTimeField(auto_now=True)

# see the following links for context
# http://stackoverflow.com/questions/1737017/django-auto-now-and-auto-now-add
# http://groups.google.com/group/django-developers/browse_thread/thread/4cd631c225cb4e52

class AutoDateTimeField(models.DateTimeField):
   '''Fixture friendly DateTimeField
   >>> created_at = AutoDateTimeField(auto_now_add=True)
   >>> updated_at = AutoDateTimeField(auto_now=True)
   '''
   def pre_save(self, model_instance, add):
      value = getattr(model_instance, self.attname)
      if value is None:
         return super(DateTimeField, self).pre_save(model_instance, add)
      return value