[req-change] Made retrieving group id robust

Author: pandafy

openwisp_controller/config/static/config/js/relevant_templates.js

@@ -105,10 +105,7 @@ django.jQuery(function ($) {
         url.searchParams.set("backend", backend);
       }
       if (isDeviceGroup() && !$(".add-form").length) {
-        // Get the group id from the URL
-        // TODO: This is fragile, consider using a more robust way to get the group id.
-        var pathParts = window.location.pathname.split("/");
-        url.searchParams.set("group_id", pathParts[pathParts.length - 3]);
+        url.searchParams.set("group_id", window._deviceGroupId);
       } else if ($('input[name="config-0-id"]').length) {
         url.searchParams.set("config_id", $('input[name="config-0-id"]').val());
       }

openwisp_controller/config/templates/admin/device_group/change_form.html

@@ -13,6 +13,7 @@
             $(document).ready( function () {
                 window._relevantTemplateUrl = "{{ relevant_template_url | safe }}";
                 window._deviceGroup = true;
+                window._deviceGroupId = "{{ original.pk }}";
                 window.bindDefaultTemplateLoading();
             })
         }) (django.jQuery);