From 7d5fd088553583931345422beee2f8c309ca5bbf Mon Sep 17 00:00:00 2001
From: Adam Goldsmith <adam@adamgoldsmith.name>
Date: Mon, 9 Sep 2024 19:15:01 -0400
Subject: [PATCH] reservations: Add generated Reservation.timespan field and
 use it for filtering

---
 .../migrations/0003_reservation_timespan.py   | 24 +++++++++++++++++++
 reservations/models.py                        | 17 +++++++------
 2 files changed, 34 insertions(+), 7 deletions(-)
 create mode 100644 reservations/migrations/0003_reservation_timespan.py

diff --git a/reservations/migrations/0003_reservation_timespan.py b/reservations/migrations/0003_reservation_timespan.py
new file mode 100644
index 0000000..19fcb1e
--- /dev/null
+++ b/reservations/migrations/0003_reservation_timespan.py
@@ -0,0 +1,24 @@
+# Generated by Django 5.1.1 on 2024-09-09 21:32
+
+import django.contrib.postgres.fields.ranges
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("reservations", "0002_externalreservation"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="reservation",
+            name="timespan",
+            field=models.GeneratedField(
+                db_persist=True,
+                expression=models.Func(
+                    models.F("start"), models.F("end"), function="tstzrange"
+                ),
+                output_field=django.contrib.postgres.fields.ranges.DateTimeRangeField(),
+            ),
+        ),
+    ]
diff --git a/reservations/models.py b/reservations/models.py
index 98afd3c..e3ffc95 100644
--- a/reservations/models.py
+++ b/reservations/models.py
@@ -3,11 +3,13 @@ from __future__ import annotations
 from typing import TYPE_CHECKING
 
 from django.contrib.auth import get_user_model
+from django.contrib.postgres.fields import DateTimeRangeField
 from django.db import models
 from django.db.models import F, Q, QuerySet
 from django.utils import timezone
 
 from model_utils.managers import InheritanceQuerySetMixin
+from psycopg.types.range import Range
 
 if TYPE_CHECKING:
     from collections.abc import Iterable
@@ -55,31 +57,32 @@ class ReservationQuerySet(InheritanceQuerySetMixin, QuerySet):
         Selects events that are after the specified datetime, including
         overlaps but excluding exactly matching endpoints.
         """
-        return self.filter(Q(start__gt=start) | Q(end__gt=start))
+        return self.filter(timespan__overlap=Range(start, None))
 
     def filter_before(self, end: datetime) -> ReservationQuerySet:
         """
         Selects events that are before the specified datetime, including
         overlaps but excluding exactly matching endpoints.
         """
-        return self.filter(Q(start__lt=end) | Q(end__lt=end))
+        return self.filter(timespan__overlap=Range(None, end))
 
     def filter_between(self, start: datetime, end: datetime) -> ReservationQuerySet:
         """
         Selects events that are between the specified datetime, including
         overlaps but excluding exactly matching endpoints.
         """
-        return self.filter(
-            Q(start__gt=start, start__lt=end)
-            | Q(end__gt=start, end__lt=end)
-            | (Q(start__lt=start) & Q(end__gt=end))
-        )
+        return self.filter(timespan__overlap=Range(start, end))
 
 
 class Reservation(models.Model):
     resources = models.ManyToManyField(Resource, blank=True)
     start = models.DateTimeField()
     end = models.DateTimeField()
+    timespan = models.GeneratedField(
+        expression=models.Func(F("start"), F("end"), function="tstzrange"),
+        output_field=DateTimeRangeField(),
+        db_persist=True,
+    )
     google_calendar_event_id = models.CharField(
         max_length=1024, null=True, blank=True, unique=True
     )