Fix PerAggregatedViewSet N+1 query issue

Author: szabozoltan69

per/drf_views.py

@@ -1075,8 +1075,27 @@ class PerAggregatedViewSet(viewsets.ReadOnlyModelViewSet):
     get_filtered_queryset = RegionRestrictedAdmin.get_filtered_queryset
 
     def get_queryset(self):
-        queryset = Overview.objects.filter(
-            id__in=Overview.objects.order_by("country_id", "-assessment_number").distinct("country_id").values("id")
+        latest_assessment = Prefetch(
+            "perassessment_set",
+            queryset=PerAssessment.objects.order_by("-id"),
+            to_attr="latest_perassessments",
+        )
+        latest_prioritization = Prefetch(
+            "formprioritization_set",
+            queryset=FormPrioritization.objects.order_by("-id"),
+            to_attr="latest_prioritizations",
+        )
+        latest_workplan = Prefetch(
+            "perworkplan_set",
+            queryset=PerWorkPlan.objects.order_by("-id"),
+            to_attr="latest_workplans",
+        )
+        queryset = (
+            Overview.objects.filter(
+                id__in=Overview.objects.order_by("country_id", "-assessment_number").distinct("country_id").values("id")
+            )
+            .select_related("country", "type_of_assessment")
+            .prefetch_related(latest_assessment, latest_prioritization, latest_workplan)
         )
         return self.get_filtered_queryset(self.request, queryset, dispatch=0)
 

per/serializers.py

@@ -628,23 +628,37 @@ class Meta:
             "translation_module_skip_auto_translation",
         )
 
+    @staticmethod
+    def _get_latest_prefetched_id(obj, attr_name, model_cls, filter_kwargs) -> typing.Optional[int]:
+        prefetched = getattr(obj, attr_name, None)
+        if prefetched is not None:
+            return prefetched[0].id if prefetched else None
+        instance = model_cls.objects.filter(**filter_kwargs).order_by("-id").first()
+        return instance.id if instance else None
+
     def get_assessment(self, obj) -> typing.Optional[int]:
-        assessment = PerAssessment.objects.filter(overview=obj).last()
-        if assessment:
-            return assessment.id
-        return None
+        return self._get_latest_prefetched_id(
+            obj,
+            "latest_perassessments",
+            PerAssessment,
+            {"overview": obj},
+        )
 
     def get_prioritization(self, obj) -> typing.Optional[int]:
-        prioritization = FormPrioritization.objects.filter(overview=obj).last()
-        if prioritization:
-            return prioritization.id
-        return None
+        return self._get_latest_prefetched_id(
+            obj,
+            "latest_prioritizations",
+            FormPrioritization,
+            {"overview": obj},
+        )
 
     def get_workplan(self, obj) -> typing.Optional[int]:
-        workplan = PerWorkPlan.objects.filter(overview=obj).last()
-        if workplan:
-            return workplan.id
-        return None
+        return self._get_latest_prefetched_id(
+            obj,
+            "latest_workplans",
+            PerWorkPlan,
+            {"overview": obj},
+        )
 
 
 class PublicPerProcessSerializer(serializers.ModelSerializer):
@@ -677,23 +691,37 @@ class Meta:
             "ns_focal_point_email",
         )
 
+    @staticmethod
+    def _get_latest_prefetched_id(obj, attr_name, model_cls, filter_kwargs) -> typing.Optional[int]:
+        prefetched = getattr(obj, attr_name, None)
+        if prefetched is not None:
+            return prefetched[0].id if prefetched else None
+        instance = model_cls.objects.filter(**filter_kwargs).order_by("-id").first()
+        return instance.id if instance else None
+
     def get_assessment(self, obj) -> typing.Optional[int]:
-        assessment = PerAssessment.objects.filter(overview=obj).last()
-        if assessment:
-            return assessment.id
-        return None
+        return self._get_latest_prefetched_id(
+            obj,
+            "latest_perassessments",
+            PerAssessment,
+            {"overview": obj},
+        )
 
     def get_prioritization(self, obj) -> typing.Optional[int]:
-        prioritization = FormPrioritization.objects.filter(overview=obj).last()
-        if prioritization:
-            return prioritization.id
-        return None
+        return self._get_latest_prefetched_id(
+            obj,
+            "latest_prioritizations",
+            FormPrioritization,
+            {"overview": obj},
+        )
 
     def get_workplan(self, obj) -> typing.Optional[int]:
-        workplan = PerWorkPlan.objects.filter(overview=obj).last()
-        if workplan:
-            return workplan.id
-        return None
+        return self._get_latest_prefetched_id(
+            obj,
+            "latest_workplans",
+            PerWorkPlan,
+            {"overview": obj},
+        )
 
 
 class QuestionResponsesSerializer(