Btukfyl

I'm writing a reservation program using the Django admin. The program will warn the user (via Django messages) when the total nights for all room changes is greater than the total nights for the reservation. So if a reservation is for 7 nights and the user enters the guest into room "A" for 4 nights and room "B" for 4 nights (totaling 8 nights) the user will see a warning. The reason for a warning and not a simple form error is that a group can have multiple rooms per night, which would make it possible for the above to occur.

The code works (below is the relevant pieces).

warn_if_rc_nights_gt_reservation_nights(), which houses the logic to warn the user, operates on the form instance (when the form is only being rendered) or the raw request.POST variables (when the form is being saved/POSTed) in order to tally up the total nights for room changes and reservations.

I'm OK with using the form instance to tally the total nights, but I have a problem with the raw POST variables, since it's more error-prone (POST variables are not clean() yet) and un-Django-like. I'd rather use a built-in class method or function to accomplish this.

I've tried to accomplish this:

• 
  Within the form.clean() method. This only works when the form is saved, so the user doesn't see the warning when simply navigating to the page.


• 
  Using various Django signals. Couldn't find a signal that had all the objects I needed to perform the action and that would fire under all circumstances.

reservations.models

class Room(models.Model):

    room_number = models.CharField(max_length=16)



class Reservation(models.Model):

    # Guest is in guest.models

    guest = models.ForeignKey(Guest, on_delete=models.CASCADE)

    check_in_date = models.DateField()

    check_out_date = models.DateField()



class RoomChange(models.Model):

    reservation = models.ForeignKey(Reservation on_delete=models.CASCADE)

    room = models.ForeignKey(Room on_delete=models.CASCADE)

    day_in = models.DateField()

    day_out = models.DateField()

reservations.admin

@admin.register(Reservation)

class ReservationAdmin(admin.ModelAdmin):

    def get_form(self, request, obj=None, **kwargs):

        # Uses a form factory to capture the request object.

        self.form = _reservation_form_factory(request)

        return super().get_form(request, obj, **kwargs)



@admin.register(Room)

class RoomAdmin(admin.ModelAdmin):

    pass



@admin.register(RoomChange)

class RoomChangeAdmin(admin.ModelAdmin):

    pass

reservations.forms

def _reservation_form_factory(request):

    class ReservationAdminForm(forms.ModelForm):

        class Meta:

            exclude = 

            model = Reservation



        def __init__(self, *args, **kwargs):

            super().__init__(*args, **kwargs)

            # Warn the user if total room change nights > reservation total nights

            warn_if_rc_nights_gt_reservation_nights(request.POST, self.instance)

    return ReservationAdminForm

So ultimately I'm asking for a simpler, less error-prone way to accomplish this task.