Get available rooms in selected dates django - mysql

Question

I am creating a project similar to a house booking system, with a few particularities (you publish the house but you can rent the rooms individually, and you can set when you are on holidays and the house is not available) in Django (rest-framework, so only API for now). The house model can be simplified to:
class House(models.Model):
title = models.CharField(max_length=127)
n_rooms = models.PositiveSmallIntegerField()
there is a calendar to save when the house is not available:
class Unavailability(models.Model):
house = models.ForeignKey(House, on_delete=models.CASCADE, related_name="house_unavailability")
unavailable_rooms = models.SmallIntegerField()
from_date = models.DateField()
to_date = models.DateField()
and a model to save when there have been bookings:
class Booking(models.Model):
house = models.ForeignKey(House, on_delete=models.CASCADE, related_name='booking')
booker = models.ForeignKey(UserProfile, on_delete=models.CASCADE)
start_date = models.DateField()
end_date = models.DateField()
n_rooms = models.PositiveSmallIntegerField(default=1)
rent = models.DecimalField(decimal_places=2, max_digits=8)
I am now trying to create an API to search the houses that have at least one room available in the selected dates (not on holidays and not booked).
I have seen some similar cases without the particularities I have and using other languages but none using Django (I am using MySQL so I could fall back to SQL if a clean solution with Django does not arise)

Answer 1

Here, I am try to write a query that will provide expected result but I am not tested that query so may syntax error will be there but I think it will help.
from django.db.models import Sum, Value, IntegerField, Q, F
from django.db.models.functions import Coalesce
from django.utils import timezone
given_start_date = timezone.now().date() # assuming
given_end_date = timezone.now().date() # assuming
houses_at_least_one_room_available = House.objects.annotate(
total_unavailable_rooms=Coalesce(
Sum("house_unavailability__unavailable_rooms", filter=Q(
house_unavailability__from_date__range=(given_start_date, given_end_date),
house_unavailability__to_date__range=(given_start_date, given_end_date)
), distinct=True),
Value(0),
output_field=IntegerField()
),
total_booked_rooms=Coalesce(
Sum("booking__n_rooms", filter=Q(
booking__start_date__range=(given_start_date, given_end_date),
booking__end_date__range=(given_start_date, given_end_date)
), distinct=True),
Value(0),
output_field=IntegerField()
),
available_rooms=F("n_rooms") - F("total_unavailable_rooms") - F("total_booked_rooms")
).filter(available_rooms__gt=0)
Here, you can update the filter query inside Sum according to your use case.