models.py

class KeyAction(models.Model):
    """Record of an action taken while using a key"""
    key = models.ForeignKey(Key, related_name='history', db_index=True)
    action = models.CharField(max_length=128, blank=False)
    notes = models.TextField(null=True)
    content_type = models.ForeignKey(ContentType)
    object_id = models.PositiveIntegerField()
    content_object = generic.GenericForeignKey('content_type', 'object_id')
    created = models.DateTimeField(auto_now_add=True)