Identify the changed fields in django post_save signal

Question

I\'m using django\'s post_save signal to execute some statements after saving the model.

class Mode(models.Model):
    name = models.CharField(max_length=5)
         


        

Answer 1

This is an old question but I've come across this situation recently and I accomplished it by doing the following:

    class Mode(models.Model):
    
        def save(self, *args, **kwargs):
            if self.pk:
                # If self.pk is not None then it's an update.
                cls = self.__class__
                old = cls.objects.get(pk=self.pk)
                # This will get the current model state since super().save() isn't called yet.
                new = self  # This gets the newly instantiated Mode object with the new values.
                changed_fields = []
                for field in cls._meta.get_fields():
                    field_name = field.name
                    try:
                        if getattr(old, field_name) != getattr(new, field_name):
                            changed_fields.append(field_name)
                    except Exception as ex:  # Catch field does not exist exception
                        pass
                kwargs['update_fields'] = changed_fields
            super().save(*args, **kwargs)

This is more effective since it catches all updates/saves from apps and django-admin.