From 9f7f2f2da5b3c842d18792ef03cb8b651bac26ea Mon Sep 17 00:00:00 2001
From: Struan Donald <struan@exo.org.uk>
Date: Thu, 11 Jan 2024 10:51:40 +0000
Subject: [PATCH] reduce number of repeated queries

move queries that get favourites and auto converted to methods that
generate dicts hence one query for all rather than one query per data
set
---
 hub/views/area.py | 49 +++++++++++++++++++++++++----------------------
 1 file changed, 26 insertions(+), 23 deletions(-)

diff --git a/hub/views/area.py b/hub/views/area.py
index fbc70204a..a978a570b 100644
--- a/hub/views/area.py
+++ b/hub/views/area.py
@@ -1,6 +1,6 @@
 from collections import defaultdict
 
-from django.db.models import Count, OuterRef, Subquery
+from django.db.models import Count
 from django.http import JsonResponse
 from django.shortcuts import get_object_or_404, redirect
 from django.views.generic import DetailView, TemplateView, View
@@ -47,23 +47,31 @@ def get_object(self):
     def get_page_title(self):
         return self.object.name
 
-    def process_dataset(self, data_set):
-        fav_sq = Subquery(
+    def get_user_favourite_datasets(self):
+        favs = (
             UserDataSets.objects.filter(
-                data_set_id=OuterRef("data_type__data_set__id"),
                 user=self.request.user,
             )
             .values("data_set_id")
             .annotate(is_favourite=Count("id"))
             .values("is_favourite")
         )
-        data_type = DataType.objects.filter(
-            data_set=data_set, area_type=self.object.area_type
-        ).first()
-        auto_converted = False
-        if data_type is not None:
-            auto_converted = data_type.auto_converted
 
+        fav_map = {}
+        for fav in favs:
+            fav_map["fav.data_set_id"] = fav["is_favourite"]
+
+        return fav_map
+
+    def get_auto_convered_datasets(self):
+        auto_converted = {}
+
+        for ds in DataType.objects.filter(area_type=self.object.area_type):
+            auto_converted[ds.data_set_id] = ds.auto_converted
+
+        return auto_converted
+
+    def process_dataset(self, data_set, favs, auto_converted):
         base_qs = AreaData.objects.filter(
             area=self.object,
             data_type__data_set=data_set,
@@ -81,33 +89,26 @@ def process_dataset(self, data_set):
             "data_type": data_set.data_type,
             "featured": data_set.featured,
             "excluded_countries": data_set.exclude_countries,
-            "auto_converted": auto_converted,
+            "auto_converted": auto_converted.get(data_set.id, False),
+            "is_favourite": favs.get(data_set.id, False),
         }
         if data_set.is_range:
             data["is_range"] = True
             data_range = base_qs.select_related("data_type").order_by("data_type__name")
 
-            data["is_favourite"] = UserDataSets.objects.filter(
-                data_set=data_set,
-                user=self.request.user,
-            ).exists()
             d = data_range.all()
             if len(d) == 0:
                 d = None
 
             data["data"] = d
         elif data_set.category == "opinion":
-            data_range = (
-                base_qs.annotate(is_favourite=fav_sq)
-                .select_related("data_type")
-                .order_by("data_type__order", "data_type__label")
+            data_range = base_qs.select_related("data_type").order_by(
+                "data_type__order", "data_type__label"
             )
 
             data["data"] = data_range.all()
         else:
-            area_data = base_qs.annotate(is_favourite=fav_sq).select_related(
-                "data_type"
-            )
+            area_data = base_qs.select_related("data_type")
             if area_data:
                 data["data"] = area_data[0]
 
@@ -190,10 +191,12 @@ def get_context_data(self, **kwargs):
 
         categories = defaultdict(list)
         indexed_categories = defaultdict(dict)
+        favs = self.get_user_favourite_datasets()
+        auto_converted = self.get_auto_convered_datasets()
         for data_set in DataSet.objects.order_by("order", "label").filter(
             areas_available=self.object.area_type
         ):
-            data = self.process_dataset(data_set)
+            data = self.process_dataset(data_set, favs, auto_converted)
 
             if data.get("data", None) is not None and data["data"]:
                 if data_set.category is not None: