Question: I have 3 models that I am dealing with here: SurveyQuestion, Update, and Notification. I use a post_save signal to create an instance of the Notification model whenever an instance of SurveyQuestion or Update was created. The Notification model has a GenericForeignKey which goes to whichever model created it. Inside the Notification model I try to use the ForeignKey to set __str__ as the title field of the instance of the model that created it. Like so: class Notification(models.Model): source_object = models.ForeignKey(ContentType, on_delete=models.CASCADE) object_id = models.PositiveIntegerField() source = GenericForeignKey("source_object", "object_id") #more stuff def __str__(self): return f'{self.source.title} notification'  I am able to create instances of SurveyQuestion and Update from the admin panel, which is then (supposed to be) creating an instance of Notification. However, when I query instances of Notification in the shell: from hotline.models import Notification notifications = Notification.objects.all() for notification in notifications: print (f"Notification object: {notification}") NoneType --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) 1 for notification in notifications: ----> 2 print (notification) File ~/ygzsey/hotline/models.py:27, in Notification.__str__(self) 26 def __str__(self): ---> 27 return f'{self.source.title} notification' AttributeError: 'NoneType' object has no attribute 'title'  When I query instances of SurveyQuestion: from hotline.models import SurveyQuestion surveys = SurveyQuestion.objects.all() for survey in surveys: print (f"Model: {survey.__class__.__name__}") Model: SurveyQuestion  When I query instances of Notification and try to print the class name of their ForeignKey field (I labled it source), I get this: for notification in notifications: print (f"Notification for {notification.source.__class__.__name__}") Notification for NoneType Notification for NoneType Notification for NoneType  So it seems that the SurveyQuestion, Update, and Notification instances are saving properly, but there is some problem with the GenericForeignKey. I had the post_save create an instance of Notification using Notification(source_object=instance, start_date=instance.start_date, end_date=instance.end_date), but that would give me an error when trying to save an instance of SurveyQuestion or Update in the admin panel: ValueError at /admin/hotline/update/add/ Cannot assign "<Update: Update - ad>": "Notification.source_object" must be a "ContentType" instance.  So I changed it to Notification(source_object=ContentType.objects.get_for_model(instance), start_date=instance.start_date, end_date=instance.end_date). My full models.py: from django.db import models from datetime import timedelta from django.utils import timezone from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation from django.contrib.contenttypes.models import ContentType from django.db.models.signals import post_save from django.dispatch import receiver def tmrw(): return timezone.now() + timedelta(days=1) class Notification(models.Model): source_object = models.ForeignKey(ContentType, on_delete=models.CASCADE) object_id = models.PositiveIntegerField() source = GenericForeignKey("source_object", "object_id") start_date = models.DateTimeField(default=timezone.now) end_date = models.DateTimeField(default=tmrw) class Meta: verbose_name = 'Notification' verbose_name_plural = f'{verbose_name}s' def __str__(self): return f'{self.source.title} notification' class Update(models.Model): title = models.CharField(max_length=25) update = models.TextField() start_date = models.DateTimeField(default=timezone.now) end_date = models.DateTimeField(default=tmrw) #notification = GenericRelation(Notification, related_query_name='notification') class Meta: verbose_name = 'Update' verbose_name_plural = f'{verbose_name}s' def __str__(self): return f'{self.__class__.__name__} - {self.title}' class SurveyQuestion(models.Model): title = models.CharField(max_length=25) question = models.TextField() start_date = models.DateTimeField(default=timezone.now) end_date = models.DateTimeField(default=tmrw) #notification = GenericRelation(Notification, related_query_name='notification') class Meta: verbose_name = 'Survey' verbose_name_plural = f'{verbose_name}s' def __str__(self): return f'{self.__class__.__name__} - {self.title}' class SurveyOption(models.Model): survey = models.ForeignKey(SurveyQuestion, on_delete=models.CASCADE, related_name='options') option = models.TextField() id = models.AutoField(primary_key=True) class Meta: verbose_name = 'Survey option' verbose_name_plural = f'{verbose_name}s' def __str__(self): return f'{self.survey.title} option #{self.id}' @receiver(post_save) def create_notification(instance, **kwargs): #""" print (f"instance: {instance}") print (f"instance.__class__: {instance.__class__}") print (f"instance.__class__.__name__: {instance.__class__.__name__}") #""" senders = ['SurveyQuestion', 'Update'] if instance.__class__.__name__ in senders: notification = Notification(source_object=ContentType.objects.get_for_model(instance), start_date=instance.start_date, end_date=instance.end_date) notification.save() post_save.connect(create_notification) 

Answer: You should use source, not source_object: Notification( source=instance, start_date=instance.start_date, end_date=instance.end_date ) A GenericForeignKey essentially combines two columns, the source_object (very bad name) that points to the type of the item the GenericForeignKey refers to, and a column that stores the primary key (or another unique column) of that object.