DBC22-5405: N+1 fix for coastal ferries

Author: wmuldergov

src/backend/apps/ferry/serializers.py

@@ -104,10 +104,13 @@ class Meta:
         )
 
     def get_routes(self, obj):
-        routes = CoastalFerryRoute.objects.filter(
-            Q(trips__stop_times__stop=obj) |
-            Q(trips__stop_times__stop__parent_stop=obj)
-        ).distinct()
+        if hasattr(obj, 'routes_list'):
+            routes = obj.routes_list
+        else:
+            routes = CoastalFerryRoute.objects.filter(
+                Q(trips__stop_times__stop=obj) |
+                Q(trips__stop_times__stop__parent_stop=obj)
+            ).distinct()
         return CoastalFerryRouteSerializer(routes, many=True).data
 
     def get_display_category(self, obj):

src/backend/apps/ferry/views.py

@@ -1,4 +1,4 @@
-from apps.ferry.models import CoastalFerryStop, Ferry
+from apps.ferry.models import CoastalFerryRoute, CoastalFerryStop, CoastalFerryStopTime, Ferry
 from apps.ferry.serializers import CoastalFerryStopAPISerializer, FerryRouteSerializer
 from apps.shared.enums import CacheKey, CacheTimeout
 from apps.shared.views import CachedListModelMixin
@@ -32,5 +32,36 @@ class CoastalFerryAPI(CachedListModelMixin):
     cache_key = CacheKey.COASTAL_FERRY_LIST
     cache_timeout = CacheTimeout.COASTAL_FERRY_LIST
 
+    def fetch_list_data(self, queryset=None):
+        stops = list(CoastalFerryStop.objects.filter(parent_stop=None))
+        stop_map = {s.id: s for s in stops}
+
+        for s in stops:
+            s.routes_list = set()
+
+        associations = CoastalFerryStopTime.objects.values_list(
+            'trip__route_id',
+            'stop_id',
+            'stop__parent_stop_id'
+        ).order_by().distinct()
+
+        all_routes = {r.id: r for r in CoastalFerryRoute.objects.all()}
+
+        for route_id, stop_id, parent_stop_id in associations:
+            route = all_routes.get(route_id)
+            if not route:
+                continue
+
+            if stop_id in stop_map:
+                stop_map[stop_id].routes_list.add(route)
+
+            if parent_stop_id and parent_stop_id in stop_map:
+                stop_map[parent_stop_id].routes_list.add(route)
+
+        for s in stops:
+            s.routes_list = sorted(list(s.routes_list), key=lambda r: r.id)
+
+        return self.get_serializer(stops, many=True).data
+
 class CoastalViewSet(CoastalFerryAPI, viewsets.ReadOnlyModelViewSet):
     pass