How to fix QuerySet' object has no attribute 'userrole_set' in django?

Question

When I Adds the specified model objects to the related object set. Like as

My view.py:

role = UserRole.objects.get(id=user_role_id)
s = SbTitle.objects.filter(user_role=1)
d = s.userrole_set.add(role) # Associates Entry role with SbTitle s.

Then QuerySet' object has no attribute 'userrole_set' error will occur. please tell me how to fix it.

MY model.py:

class SbTitle(models.Model):
    sb_title = models.CharField(max_length = 100, blank=True, null=True)
    user_role = models.ForeignKey(UserRole, blank=True, null=True, on_delete=models.CASCADE)


    def __str__(self):
        return self.sb_title