DBC22-5405: N+1 issues in ferry API

Author: wmuldergov

src/backend/apps/ferry/serializers.py

@@ -79,7 +79,10 @@ class Meta:
         )
 
     def get_vessels(self, obj):
-        vessels = Ferry.objects.filter(route_id=obj.route_id).order_by("priority")
+        if hasattr(obj, 'vessels_list'):
+            vessels = obj.vessels_list
+        else:
+            vessels = Ferry.objects.filter(route_id=obj.route_id).order_by("priority")
         return FerryVesselSerializer(vessels, many=True).data
 
     def get_id(self, obj):

src/backend/apps/ferry/views.py

@@ -6,11 +6,23 @@
 
 
 class FerryAPI(CachedListModelMixin):
-    queryset = Ferry.objects.distinct('route_id')
+    queryset = Ferry.objects.all()
     serializer_class = FerryRouteSerializer
     cache_key = CacheKey.FERRY_LIST
     cache_timeout = CacheTimeout.FERRY_LIST
 
+    def fetch_list_data(self, queryset=None):
+        qs = Ferry.objects.all().order_by('route_id', 'priority')
+        routes = {}
+        for ferry in qs:
+            if ferry.route_id not in routes:
+                ferry.vessels_list = []
+                routes[ferry.route_id] = ferry
+
+            routes[ferry.route_id].vessels_list.append(ferry)
+
+        return self.get_serializer(list(routes.values()), many=True).data
+
 class FerryViewSet(FerryAPI, viewsets.ReadOnlyModelViewSet):
     pass