Question

I am building a django query to make apartment reservations. User enters start and end date and the db is checked too see if a clashing reservation already exists. That is to say, if any part of the daterange of the reservation overlaps with an existing reservation’s daterange.

I have a system that works, but it hits the DB 3 times, and I’m sure it could be done in 1 (with OR condition in the query?). Can I optimise the following?:

        bookings = Booking.objects.filter(  arrival_date__range=(query_start, query_end)  )
        if len(bookings) > 0:
            status = 'failure'
        else:
            bookings = Booking.objects.filter(  departure_date__range=(query_start, query_end)  )
            if len(bookings) > 0:
                status = 'failure'
            else:
                bookings = Booking.objects.filter( arrival_date__lte=query_start ).filter( departure_date__gte = query_end  )
                if len(bookings) > 0:
                    status = 'failure'

Many thanks for feedback

Answer 1

This is possible by ORing querysets and using th Q object, with something like this:

from django.db.models import Q

apts_booked1 = Rental.objects.values_list('id', flat=True).select_related().filter(  Q(booking__arrival_date__range=(query_start, query_end) )  | Q(booking__departure_date__range=(query_start, query_end) )).distinct('id')
apts_booked2 = Rental.objects.values_list('id', flat=True).select_related().filter(booking__arrival_date__lte=query_start).filter( booking__departure_date__gte = query_end ).distinct('id')
apts_booked = apts_booked1 | apts_booked2

This should only hit the db once.