Fixed N+1 queries issue in /api/v1/bed/ (#1908)

* Fixed N+1 queries issue in /api/v1/bed/

* Feat: PR review changes for issue #1338

Removed is_occupied property from Bed model as it is not used anywhere

Annotated is_occupied field in the queryset instead of _is_occupied

* Feat: PR review changes

Changed is_occupied from SerializerMethodField to Boolean Field

* Feat: PR Review Changes

Annotated is_occupied field irrespective of action

* Added the test case for listing beds API

* add comment explaining number of queries

---------

Co-authored-by: Aakash Singh <[email protected]>

care/facility/api/viewsets/bed.py

@@ -1,6 +1,6 @@
 from django.core.exceptions import ValidationError as DjangoValidationError
 from django.db import IntegrityError, transaction
-from django.db.models import OuterRef, Subquery
+from django.db.models import Exists, OuterRef, Subquery
 from django_filters import rest_framework as filters
 from drf_spectacular.utils import extend_schema, extend_schema_view
 from rest_framework import filters as drf_filters
@@ -50,7 +50,7 @@ class BedViewSet(
 ):
     queryset = (
         Bed.objects.all()
-        .select_related("facility", "location")
+        .select_related("facility", "location", "location__facility")
         .order_by("-created_date")
     )
     serializer_class = BedSerializer
@@ -63,6 +63,15 @@ class BedViewSet(
     def get_queryset(self):
         user = self.request.user
         queryset = self.queryset
+
+        queryset = queryset.annotate(
+            is_occupied=Exists(
+                ConsultationBed.objects.filter(
+                    bed__id=OuterRef("id"), end_date__isnull=True
+                )
+            )
+        )
+
         if user.is_superuser:
             pass
         elif user.user_type >= User.TYPE_VALUE_MAP["StateLabAdmin"]:

care/facility/models/bed.py

@@ -40,10 +40,6 @@ class Meta:
             )
         ]
 
-    @property
-    def is_occupied(self) -> bool:
-        return ConsultationBed.objects.filter(bed=self, end_date__isnull=True).exists()
-
     def __str__(self):
         return self.name
 

care/facility/tests/test_bed_api.py

@@ -0,0 +1,38 @@
+from rest_framework import status
+from rest_framework.test import APITestCase
+
+from care.facility.models import Bed
+from care.utils.tests.test_utils import TestUtils
+
+
+class BedViewSetTestCase(TestUtils, APITestCase):
+    @classmethod
+    def setUpTestData(cls) -> None:
+        cls.state = cls.create_state()
+        cls.district = cls.create_district(cls.state)
+        cls.local_body = cls.create_local_body(cls.district)
+        cls.super_user = cls.create_super_user("su", cls.district)
+        cls.facility = cls.create_facility(cls.super_user, cls.district, cls.local_body)
+        cls.asset_location = cls.create_asset_location(cls.facility)
+        cls.user = cls.create_user("staff", cls.district, home_facility=cls.facility)
+        cls.patient = cls.create_patient(
+            cls.district, cls.facility, local_body=cls.local_body
+        )
+
+    def setUp(self) -> None:
+        super().setUp()
+        self.bed1 = Bed.objects.create(
+            name="bed1", location=self.asset_location, facility=self.facility
+        )
+        self.bed2 = Bed.objects.create(
+            name="bed2", location=self.asset_location, facility=self.facility
+        )
+        self.bed3 = Bed.objects.create(
+            name="bed3", location=self.asset_location, facility=self.facility
+        )
+
+    def test_list_beds(self):
+        # includes 3 queries for auth and 1 for pagination count
+        with self.assertNumQueries(5):
+            response = self.client.get("/api/v1/bed/")
+        self.assertEqual(response.status_code, status.HTTP_200_OK)