Fix multiple user queries n+1 issue

Author: szabozoltan69

api/drf_views.py

@@ -1,6 +1,6 @@
 from datetime import timedelta
 
-from django.contrib.auth.models import User
+from django.contrib.auth.models import Group, User
 from django.db import models
 from django.db.models import (
     Avg,
@@ -1297,7 +1297,23 @@ class UsersViewset(viewsets.ReadOnlyModelViewSet):
     filterset_class = UserFilterSet
 
     def get_queryset(self):
-        return User.objects.filter(is_active=True)
+
+        return (
+            User.objects.select_related(
+                "profile",
+                "profile__country",
+            )
+            .prefetch_related("subscription")
+            .annotate(
+                is_ifrc_admin=models.Exists(
+                    Group.objects.filter(
+                        name__iexact="IFRC Admins",
+                        user=OuterRef("pk"),
+                    )
+                )
+            )
+            .filter(is_active=True)
+        )
 
 
 class GlobalEnumView(APIView):

api/serializers.py

@@ -1616,7 +1616,7 @@ class Meta:
 class UserSerializer(ModelSerializer):
     profile = ProfileSerializer()
     subscription = MiniSubscriptionSerializer(many=True)
-    is_ifrc_admin = serializers.SerializerMethodField()
+    is_ifrc_admin = serializers.BooleanField(read_only=True)
 
     class Meta:
         model = User
@@ -1654,9 +1654,11 @@ def update(self, instance, validated_data):
         instance.save()
         return instance
 
-    @staticmethod
-    def get_is_ifrc_admin(obj) -> bool:
-        return obj.groups.filter(name__iexact="IFRC Admins").exists()
+
+# Instead of the below method we use the serializer's annotate tag:
+#    @staticmethod
+#    def get_is_ifrc_admin(obj) -> bool:
+#        return obj.groups.filter(name__iexact="IFRC Admins").exists()
 
 
 class UserNameSerializer(UserSerializer):