[fix] Add group-scoped cache invalidation task for device group context change

Replace the org-wide invalidate_controller_views_cache call in
DeviceGroup.save() with a new group-scoped task
invalidate_controller_views_for_group that only clears
DeviceChecksumView entries for devices belonging to that group,
avoiding unnecessary invalidation of unrelated devices and VPN caches.

Also adds assertion in test_status_update_on_group_variable_change to
verify the scoped task is enqueued with the correct group_id.

Fixes openwisp#1070

Author: mn-ram

openwisp_controller/config/base/device_group.py

@@ -17,7 +17,7 @@
 from ..sortedm2m.fields import SortedManyToManyField
 from ..tasks import (
     bulk_invalidate_config_get_cached_checksum,
-    invalidate_controller_views_cache,
+    invalidate_controller_views_for_group,
 )
 from .config import TemplatesThrough
 
@@ -91,7 +91,7 @@ def save(
             bulk_invalidate_config_get_cached_checksum.delay(
                 {"device__group_id": str(self.id)}
             )
-            invalidate_controller_views_cache.delay(str(self.organization_id))
+            invalidate_controller_views_for_group.delay(str(self.id))
 
     def get_context(self):
         return deepcopy(self.context)

openwisp_controller/config/tasks.py

@@ -217,3 +217,21 @@ def invalidate_controller_views_cache(organization_id):
         Vpn.objects.filter(organization_id=organization_id).only("id").iterator()
     ):
         GetVpnView.invalidate_get_vpn_cache(vpn)
+
+
+@shared_task(base=OpenwispCeleryTask)
+def invalidate_controller_views_for_group(group_id):
+    """
+    Invalidates the DeviceChecksumView cache only for devices in the given group.
+
+    Unlike invalidate_controller_views_cache, this is scoped to a single device
+    group and does not invalidate VPN caches.
+    """
+    from .controller.views import DeviceChecksumView
+
+    Device = load_model("config", "Device")
+
+    for device in (
+        Device.objects.filter(group_id=group_id).only("id").iterator()
+    ):
+        DeviceChecksumView.invalidate_get_device_cache(device)

openwisp_controller/config/tests/test_device.py

@@ -480,7 +480,10 @@ def test_status_update_on_group_variable_change(self):
         c2.set_status_applied()
         dg.context = {"ssid": "OrgA"}
         dg.full_clean()
-        dg.save()
+        patch_path = "openwisp_controller.config.base.device_group.invalidate_controller_views_for_group"
+        with mock.patch(patch_path) as mocked_task:
+            dg.save()
+            mocked_task.delay.assert_called_once_with(str(dg.id))
         c1.refresh_from_db()
         c2.refresh_from_db()
         with self.subTest("affected config changes to modified"):