class MyObjectHistory(models.Model):
    created_by = models.ForeignKey(User, on_delete=models.DO_NOTHING, editable=False,null=True,blank=True)
    save_date = models.DateTimeField(auto_now=True)
    my_object = models.ForeignKey(MyObject, on_delete=models.CASCADE)
    notes = models.TextField(blank=True, null=True)