[Python] Cannot assign "": "" must be a "User" instance

I'm making a project using the Django framework and is creating a website and is encountering this error:

Cannot assign "<User: >": "Booking.teacher" must be a "User" instance.
​

this is my models.py for the booking:

class Booking(models.Model):
room = models.ForeignKey(Room, on_delete=models.CASCADE)
teacher = models.ForeignKey(User, on_delete=models.CASCADE, limit_choices_to={'role': 'teacher'})
date = models.DateField()
start_time = models.TimeField()
end_time = models.TimeField()
purpose = models.CharField(max_length=255, blank=True, null=True)

class Meta:
unique_together = ('room', 'date', 'start_time', 'end_time')

def __str__(self):
return f"{self.room.name} - {self.date} ({self.start_time} to {self.end_time})"


this is my forms.py:

class BookingForm(forms.ModelForm):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
self.fields['teacher'].queryset = User.objects.filter(groups__name='teacher') # Filter teachers

class Meta:
model = Booking
fields = ['room', 'date', 'start_time', 'end_time', 'teacher']
widgets = {
'date': forms.DateInput(attrs={'type': 'date', 'class': 'form-control'}),
'start_time': forms.TimeInput(attrs={'type': 'time', 'class': 'form-control'}), # Updated to start_time
'end_time': forms.TimeInput(attrs={'type': 'time', 'class': 'form-control'}), # Added end_time
'room': forms.TextInput(attrs={'class': 'form-control'}),
'teacher': forms.Select(attrs={'class': 'form-control'}),
}

def clean(self):
cleaned_data = super().clean()
room = cleaned_data.get('room')
date = cleaned_data.get('date')
start_time = cleaned_data.get('start_time')
end_time = cleaned_data.get('end_time')


# Check for booking conflicts
if Booking.objects.filter(room=room, date=date, start_time=start_time, end_time=end_time).exists():

raise ValidationError('This room is already booked for the selected date and time.')

return cleaned_data


and this is my views:

def booking_calendar(request):
rooms = Room.objects.all() # Fetch all rooms for the dropdown
bookings = Booking.objects.all()

if request.method == 'POST':
form = BookingForm(request.POST)
if form.is_valid():
booking = form.save(commit=False)
booking.teacher = request.user if request.user.groups.filter(name='teacher').exists() else None # Assign the current user as the teacher if they are a teacher
if booking.teacher is None:
messages.error(request, 'You do not have permission to create a booking as a teacher.') # Error message


booking.save()
messages.success(request, 'Booking created successfully!')
return redirect('booking_calendar')
else:
messages.error(request, 'There was an error in your booking. Please check the form.')

else:
form = BookingForm()

return render(request, 'booking_calendar.html', {'bookings': bookings, 'form': form, 'rooms': rooms}) # Pass rooms to the template


I tested to see if the form works and reflects into the database in making a booking but there's only this error Cannot assign "<User: mhar>": "Booking.teacher" must be a "User" instance. I'm a beginner in this and is my first time seeing this error. I'm stuck in this error pls help

Continue reading...