[fix] Fixed sorting issue in templates

Using the 'sort_value' of the 'through_model', created a subquery
which annotates a sort_value and selected field to each template.
The sort_value is used for ordering the templates and also for
checking if template is selected or not using a large default value
which  happens if template is not selected for a device config or
group.

Signed-off-by: DragnEmperor <[email protected]>

Author: DragnEmperor

openwisp_controller/config/views.py

@@ -2,7 +2,9 @@
 from copy import deepcopy
 from uuid import UUID
 
+from django.db import models as django_models
 from django.db.models import Q
+from django.db.models.functions import Coalesce
 from django.http import HttpResponse, JsonResponse
 from django.utils import timezone
 from django.utils.module_loading import import_string
@@ -31,34 +33,58 @@ def get_relevant_templates(request, organization_id):
     if not user.is_superuser and not user.is_manager(organization_id):
         return HttpResponse(status=403)
     org = get_object_or_404(Organization, pk=organization_id, is_active=True)
+    org_filters = Q(organization_id=org.pk) | Q(organization_id=None)
     filter_options = {}
     if backend:
         filter_options.update(backend=backend)
     else:
         filter_options.update(required=False, default=False)
+    sort_value_subquery = None
+    # fetch the selected templates for the device or group by creating a subquery.
+    # through_model and lookup_field are set based on the presence of device_id or
+    # group_id. we need through_model as `sort_value` is a field of the through model.
+    # the subquery will be used to annotate the queryset with the sort_value
+    # of the selected templates.
+    if device_id and (lookup := Config.objects.filter(device_id=device_id).first()):
+        through_model = Config.templates.through
+        lookup_field = "config_id"
+    if group_id and (
+        lookup := DeviceGroup.objects.filter(Q(pk=group_id) & (org_filters)).first()
+    ):
+        through_model = DeviceGroup.templates.through
+        lookup_field = "devicegroup_id"
+    if device_id or group_id:
+        sort_value_subquery = django_models.Subquery(
+            through_model.objects.filter(
+                **{lookup_field: lookup.id}, template_id=django_models.OuterRef('pk')
+            ).values('sort_value')[:1],
+            output_field=django_models.IntegerField(),
+        )
+    # annotated a selected field which is True based on sort_value
+    # if sort_value is 9999 then selected is False else True
     queryset = (
         Template.objects.filter(**filter_options)
-        .filter(Q(organization_id=org.pk) | Q(organization_id=None))
+        .filter(org_filters)
+        .annotate(
+            sort_value=Coalesce(sort_value_subquery, django_models.Value(9999)),
+            selected=django_models.Case(
+                django_models.When(sort_value=9999, then=django_models.Value(False)),
+                default=django_models.Value(True),
+                output_field=django_models.BooleanField(),
+            ),
+        )
+        .order_by('sort_value')
         .only('id', 'name', 'backend', 'default', 'required')
     )
-    # for checking which templates are enabled for given device or group
-    selected_templates = []
-    if device_id:
-        selected_templates = Config.objects.filter(device_id=device_id).values_list(
-            'templates__id', flat=True
-        )
-    if group_id:
-        selected_templates = DeviceGroup.objects.filter(
-            pk=group_id, organization_id=organization_id
-        ).values_list('templates__id', flat=True)
+
     relevant_templates = {}
     for template in queryset:
         relevant_templates[str(template.pk)] = dict(
             name=template.name,
             backend=template.get_backend_display(),
             default=template.default,
             required=template.required,
-            selected=template.pk in selected_templates,
+            selected=template.selected,
         )
     return JsonResponse(relevant_templates)