the django pre-delete signal is not updating the foreign key field of the instance

The book in your delete view is a different Python object than the in your signal handler. The Python object does not magically learn that the underlying db representation has changed. You could call refresh_from_db before printing:


Or just make num_of_likes an dynamically evaluated property altogether and you won’t have to worry about the integrity of your denormalized data:

class Book(models.Model):
    def num_of_likes(self):
        return self.like_set.count()

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