Fix facility n+1

care/facility/api/serializers/facility.py

@@ -52,9 +52,13 @@ class FacilityBasicInfoSerializer(serializers.ModelSerializer):
     bed_count = serializers.SerializerMethodField()
 
     def get_bed_count(self, facility):
+        if hasattr(facility, "bed_count"):
+            return facility.bed_count
         return Bed.objects.filter(facility=facility).count()
 
     def get_patient_count(self, facility):
+        if hasattr(facility, "patientregistrations_count"):
+            return facility.patientregistrations_count
         return PatientRegistration.objects.filter(
             facility=facility, is_active=True
         ).count()

care/facility/api/viewsets/facility.py

@@ -1,4 +1,6 @@
 from django.conf import settings
+from django.db.models import Count, OuterRef, Subquery
+from django.db.models.functions import Coalesce
 from django_filters import rest_framework as filters
 from djqscsv import render_to_csv_response
 from drf_spectacular.utils import extend_schema, extend_schema_view
@@ -21,7 +23,9 @@
     FacilityPatientStatsHistory,
     HospitalDoctors,
 )
+from care.facility.models.bed import Bed
 from care.facility.models.facility import FacilityUser
+from care.facility.models.patient import PatientRegistration
 from care.users.models import User
 
 
@@ -71,8 +75,31 @@ class FacilityViewSet(
 ):
     """Viewset for facility CRUD operations."""
 
-    queryset = Facility.objects.all().select_related(
-        "ward", "local_body", "district", "state"
+    patient_registration_count_subquery = Subquery(
+        PatientRegistration.objects.filter(facility=OuterRef("pk"))
+        .values("facility")
+        .annotate(count=Count("id"))
+        .values("count")
+    )
+    bed_count_subquery = Subquery(
+        Bed.objects.filter(facility=OuterRef("pk"))
+        .values("facility")
+        .annotate(count=Count("id"))
+        .values("count")
+    )
+
+    queryset = (
+        Facility.objects.all()
+        .select_related(
+            "ward",
+            "local_body",
+            "district",
+            "state",
+        )
+        .annotate(
+            patientregistrations_count=Coalesce(patient_registration_count_subquery, 0)
+        )
+        .annotate(bed_count=Coalesce(bed_count_subquery, 0))
     )
     permission_classes = (
         IsAuthenticated,

care/facility/tests/test_facility_api.py

@@ -91,3 +91,25 @@ def test_delete_with_active_patients(self):
         self.client.force_authenticate(user=state_admin)
         response = self.client.delete(f"/api/v1/facility/{facility.external_id}/")
         self.assertIs(response.status_code, status.HTTP_400_BAD_REQUEST)
+
+    def test_listing_db_queries(self):
+        """This test case is to test the get api endpoint for facility and to ensure that only one db query is made for fetching the list of facilities"""
+        facility_1 = self.create_facility(
+            self.super_user, self.district, self.local_body
+        )
+        facility_2 = self.create_facility(
+            self.super_user, self.district, self.local_body
+        )
+        facility_3 = self.create_facility(
+            self.super_user, self.district, self.local_body
+        )
+        self.create_patient(self.district, facility_1)
+        self.create_patient(self.district, facility_2)
+        self.create_patient(self.district, facility_3)
+
+        self.client.force_authenticate(user=self.super_user)
+
+        with self.assertNumQueries(2):
+            response = self.client.get("/api/v1/facility/")
+
+        self.assertIs(response.status_code, status.HTTP_200_OK)