old_contents: from __future__ import unicode_literals
  
  from django.conf import settings
  from django.contrib.contenttypes.generic import GenericForeignKey
  from django.contrib.contenttypes.models import ContentType
  from django.db import models
  
  from django_fsm.signals import post_transition
  
  from .managers import StateLogManager
  
  
  class StateLog(models.Model):
      timestamp = models.DateTimeField(auto_now_add=True)
      by = models.ForeignKey(getattr(settings, 'AUTH_USER_MODEL', 'auth.User'), blank=True, null=True)
      state = models.CharField(max_length=255, db_index=True)
      transition = models.CharField(max_length=255)
  
      content_type = models.ForeignKey(ContentType)
      object_id = models.PositiveIntegerField(db_index=True)
      content_object = GenericForeignKey('content_type', 'object_id')
  
      objects = StateLogManager()
  
  
  def transition_callback(sender, instance, name, source, target, **kwargs):
      state_log = StateLog(
          by=getattr(instance, 'by', None),
          state=target,
          transition=name,
          content_object=instance,
      )
      state_log.save()
  
  
  post_transition.connect(transition_callback)
  
new_contents: from __future__ import unicode_literals
  
  from django.conf import settings
  from django.contrib.contenttypes.generic import GenericForeignKey
  from django.contrib.contenttypes.models import ContentType
  from django.db import models
  from django.utils.timezone import now
  
  from django_fsm.signals import post_transition
  
  from .managers import StateLogManager
  
  
  class StateLog(models.Model):
      timestamp = models.DateTimeField(default=now)
      by = models.ForeignKey(getattr(settings, 'AUTH_USER_MODEL', 'auth.User'), blank=True, null=True)
      state = models.CharField(max_length=255, db_index=True)
      transition = models.CharField(max_length=255)
  
      content_type = models.ForeignKey(ContentType)
      object_id = models.PositiveIntegerField(db_index=True)
      content_object = GenericForeignKey('content_type', 'object_id')
  
      objects = StateLogManager()
  
  
  def transition_callback(sender, instance, name, source, target, **kwargs):
      state_log = StateLog(
          by=getattr(instance, 'by', None),
          state=target,
          transition=name,
          content_object=instance,
      )
      state_log.save()
  
  
  post_transition.connect(transition_callback)
  
subject: Switch from auto_now_add=True to default=now