Cannot query "sabbir": Must be "User" instance

Question

I mean when a doctor uploads a file, the patients that are under that doctor can see that file. In the same way when a patient uploads his prescription only that doctor can see.

views.py
def practitioner_tab(request, practitioner_id):
   client = Appointment.objects.get(id=practitioner_id)
   practitioner = Profile.objects.get(user=client.practitioner)
   notes = AddNote.objects.filter(user=client.practitioner)        
   appointments=Appointment.objects.filter(user=client.practitioner)
   context = {
   'client': client,
   'practitioner': practitioner,
   'notes': notes,
   'appointments': appointments,
}
return render(request, 'client/practitioner_tab.html', context)

models.py
   class Profile(models.Model):
   phone = models.CharField(max_length=50, blank=True, null=True)
   avatar = models.ImageField(max_length=50, blank=True, null=True, 
   upload_to='practitioner/avatar')
   start_date = models.DateTimeField(auto_now_add=True)
   user = models.OneToOneField(User, on_delete=models.CASCADE)

   def __str__(self):
       return self.user.username


   class Appointment(models.Model):
     Appointments = [
     ('audio', 'audio'),
     ('video', 'video'),
     ]
     practitioner = models.ForeignKey(Profile, 
     on_delete=models.CASCADE, related_name='practitioner')
     time = models.DateTimeField()
     appointment = models.CharField(max_length=100, 
     choices=Appointments)
     user = models.ForeignKey(User, on_delete=models.CASCADE)


     def __str__(self):
        return self.user.username