chore(dref): optimise active dref query

Author: susilnem

assets

@@ -208,15 +208,25 @@ class MiniDrefSerializer(serializers.ModelSerializer):
     type_of_dref_display = serializers.CharField(source="get_type_of_dref_display", read_only=True)
     status_display = serializers.CharField(source="get_status_display", read_only=True)
     country_details = MiniCountrySerializer(source="country", read_only=True)
-    has_ops_update = serializers.SerializerMethodField()
-    has_final_report = serializers.SerializerMethodField()
+    starting_language = serializers.CharField(read_only=True)
+    # Manually added fields
     application_type = serializers.SerializerMethodField()
     application_type_display = serializers.SerializerMethodField()
-    unpublished_op_update_count = serializers.SerializerMethodField()
-    unpublished_final_report_count = serializers.SerializerMethodField()
-    operational_update_details = serializers.SerializerMethodField()
-    final_report_details = serializers.SerializerMethodField()
-    starting_language = serializers.CharField(read_only=True)
+    # Annotate values from queryset
+    has_ops_update = serializers.BooleanField(read_only=True)
+    has_final_report = serializers.BooleanField(read_only=True)
+    unpublished_op_update_count = serializers.IntegerField(read_only=True)
+    unpublished_final_report_count = serializers.IntegerField(read_only=True)
+    # Prefetched data
+    operational_update_details = MiniOperationalUpdateActiveSerializer(
+        source="prefetched_operational_updates",
+        many=True,
+        read_only=True,
+    )
+    final_report_details = MiniDrefFinalReportActiveSerializer(
+        source="dreffinalreport",
+        read_only=True,
+    )
 
     class Meta:
         model = Dref
@@ -250,39 +260,14 @@ class Meta:
             "starting_language",
         ]
 
-    @extend_schema_field(MiniOperationalUpdateActiveSerializer(many=True))
-    def get_operational_update_details(self, obj):
-        queryset = DrefOperationalUpdate.objects.filter(dref_id=obj.id).order_by("-created_at")
-        return MiniOperationalUpdateActiveSerializer(queryset, many=True).data
-
-    @extend_schema_field(MiniDrefFinalReportActiveSerializer)
-    def get_final_report_details(self, obj):
-        queryset = DrefFinalReport.objects.filter(dref_id=obj.id).first()
-        return MiniDrefFinalReportActiveSerializer(queryset).data
-
-    def get_has_ops_update(self, obj) -> bool:
-        op_count_count = obj.drefoperationalupdate_set.count()
-        if op_count_count > 0:
-            return True
-        return False
-
-    def get_has_final_report(self, obj) -> bool:
-        if hasattr(obj, "dreffinalreport"):
-            return True
-        return False
-
-    def get_application_type(self, obj) -> str:
+    @extend_schema_field(serializers.CharField())
+    def get_application_type(self, _) -> str:
         return "DREF"
 
-    def get_application_type_display(self, obj) -> str:
+    @extend_schema_field(serializers.CharField())
+    def get_application_type_display(self, _) -> str:
         return gettext("DREF application")
 
-    def get_unpublished_op_update_count(self, obj) -> int:
-        return DrefOperationalUpdate.objects.filter(dref_id=obj.id).exclude(status=Dref.Status.APPROVED).count()
-
-    def get_unpublished_final_report_count(self, obj) -> int:
-        return DrefFinalReport.objects.filter(dref_id=obj.id).exclude(status=Dref.Status.APPROVED).count()
-
 
 class PlannedInterventionSerializer(
     NestedCreateMixin,

dref/serializers.py

@@ -4,7 +4,9 @@
 
 import django.utils.timezone as timezone
 from django.contrib.auth.models import Permission
+from django.contrib.gis.db.models import Count, Exists, OuterRef, Q
 from django.db import models, transaction
+from django.db.models.query import Prefetch
 from django.http import HttpResponse
 from django.templatetags.static import static
 from django.utils.translation import gettext
@@ -53,7 +55,7 @@
 logger = logging.getLogger(__name__)
 
 
-def filter_dref_queryset_by_user_access(user, queryset):
+def filter_dref_queryset_by_user_access(user, queryset: models.QuerySet) -> models.QuerySet[Dref]:
     if user.is_superuser:
         return queryset
     # Check if regional admin
@@ -344,16 +346,43 @@ class ActiveDrefOperationsViewSet(viewsets.ReadOnlyModelViewSet):
     serializer_class = MiniDrefSerializer
     permission_classes = [permissions.IsAuthenticated, DenyGuestUserPermission]
     filterset_class = ActiveDrefFilterSet
+
     queryset = (
-        Dref.objects.prefetch_related("planned_interventions", "needs_identified", "national_society_actions", "users")
+        Dref.objects.select_related(
+            "country",
+        )
+        .prefetch_related(
+            Prefetch(
+                "drefoperationalupdate_set",
+                queryset=DrefOperationalUpdate.objects.select_related("country").order_by("-created_at"),
+                to_attr="prefetched_operational_updates",
+            ),
+            "dreffinalreport__country",
+        )
         .order_by("-created_at")
         .filter(is_active=True)
-        .distinct()
     )
 
     def get_queryset(self):
-        # user = self.request.user
-        return filter_dref_queryset_by_user_access(self.request.user, super().get_queryset()).order_by("-created_at")
+        return filter_dref_queryset_by_user_access(
+            self.request.user,
+            super().get_queryset(),
+        ).annotate(
+            has_ops_update=Exists(
+                DrefOperationalUpdate.objects.filter(dref=OuterRef("pk")),
+            ),
+            unpublished_op_update_count=Count(
+                "drefoperationalupdate",
+                filter=~Q(drefoperationalupdate__status=Dref.Status.APPROVED),
+            ),
+            has_final_report=Exists(
+                DrefFinalReport.objects.filter(dref=OuterRef("pk")),
+            ),
+            unpublished_final_report_count=Count(
+                "dreffinalreport",
+                filter=~Q(dreffinalreport__status=Dref.Status.APPROVED),
+            ),
+        )
 
 
 class DrefShareView(views.APIView):