Optimized number of queries on Projects page

cvat/apps/engine/serializers.py

@@ -1344,10 +1344,12 @@ class Meta:
 
     def to_representation(self, instance):
         response = super().to_representation(instance)
-        task_subsets = set(instance.tasks.values_list('subset', flat=True))
+        subsets = (task.subset for task in instance.tasks.all())
+        dimensions = (task.dimension for task in instance.tasks.all())
+        task_subsets = set(subsets)
         task_subsets.discard('')
         response['task_subsets'] = list(task_subsets)
-        response['dimension'] = instance.tasks.first().dimension if instance.tasks.count() else None
+        response['dimension'] = next(dimensions, None)
         return response
 
 class ProjectWriteSerializer(serializers.ModelSerializer):

cvat/apps/engine/views.py

@@ -289,6 +289,8 @@ def get_queryset(self):
         if self.action == 'list':
             perm = ProjectPermission.create_scope_list(self.request)
             queryset = perm.filter(queryset)
+        elif self.action == 'preview':
+            queryset = Project.objects.filter(**self.kwargs)
         return queryset
 
     @transaction.atomic
@@ -625,7 +627,7 @@ def append_backup_chunk(self, request, file_id):
     def preview(self, request, pk):
         self._object = self.get_object() # call check_object_permissions as well
 
-        first_task = self._object.tasks.order_by('-id').first()
+        first_task = self._object.tasks.select_related('data').order_by('-id').first()
         if not first_task:
             return HttpResponseNotFound('Project image preview not found')
 
@@ -864,6 +866,8 @@ def get_queryset(self):
         if self.action == 'list':
             perm = TaskPermission.create_scope_list(self.request)
             queryset = perm.filter(queryset)
+        elif self.action == 'preview':
+            queryset = Task.objects.filter(**self.kwargs).select_related('data')
 
         return queryset