fix(dcim): Refresh stale CablePath references during serialization

Cable edits can delete and recreate CablePath rows while endpoint
instances remain in memory. Deferred event serialization can then
encounter a stale `_path` reference and raise `CablePath.DoesNotExist`.

Refresh stale `_path` references through `PathEndpoint.path` and route
internal callers through that accessor. Update `EventContext` to track
the latest serialization source for coalesced duplicate enqueues, while
eagerly freezing delete-event payloads before row removal.

Also avoid mutating `event_rule.action_data` when merging the event
payload.

Fixes #21498

netbox/dcim/api/serializers_/base.py

@@ -38,7 +38,19 @@ class ConnectedEndpointsSerializer(serializers.ModelSerializer):
 
     @extend_schema_field(serializers.BooleanField)
     def get_connected_endpoints_reachable(self, obj):
-        return obj._path and obj._path.is_complete and obj._path.is_active
+        """
+        Determines if the connected endpoints are reachable through a cable path.
+
+        This method checks whether there is a valid and active cable path that
+        connects the endpoints. It evaluates both the completeness and active
+        status of the path to determine reachability.
+        """
+        # Use the public `path` accessor rather than dereferencing `_path`
+        # directly. `path` already handles the stale in-memory relation case
+        # that can occur while CablePath rows are rebuilt during cable edits.
+        if path := obj.path:
+            return path.is_complete and path.is_active
+        return False
 
 
 class PortSerializer(serializers.ModelSerializer):

netbox/dcim/models/device_components.py

@@ -2,7 +2,7 @@ from functools import cached_property
 
 from django.contrib.contenttypes.fields import GenericForeignKey, GenericRelation
 from django.contrib.postgres.fields import ArrayField
-from django.core.exceptions import ValidationError
+from django.core.exceptions import ObjectDoesNotExist, ValidationError
 from django.core.validators import MaxValueValidator, MinValueValidator
 from django.db import models
 from django.db.models import Sum
@@ -298,20 +298,24 @@ class CabledObjectModel(models.Model):
 
 class PathEndpoint(models.Model):
     """
-    An abstract model inherited by any CabledObjectModel subclass which represents the end of a CablePath; specifically,
-    these include ConsolePort, ConsoleServerPort, PowerPort, PowerOutlet, Interface, and PowerFeed.
+    An abstract model inherited by any CabledObjectModel subclass which
+    represents the end of a CablePath; specifically, these include
+    ConsolePort, ConsoleServerPort, PowerPort, PowerOutlet, Interface, and
+    PowerFeed.
 
-    `_path` references the CablePath originating from this instance, if any. It is set or cleared by the receivers in
-    dcim.signals in response to changes in the cable path, and complements the `origin` GenericForeignKey field on the
-    CablePath model. `_path` should not be accessed directly; rather, use the `path` property.
-
-    `connected_endpoints()` is a convenience method for returning the destination of the associated CablePath, if any.
+    `_path` references the CablePath originating from this instance, if any.
+    It is set or cleared by the receivers in dcim.signals in response to
+    changes in the cable path, and complements the `origin` GenericForeignKey
+    field on the CablePath model. `_path` should not be accessed directly;
+    rather, use the `path` property. `connected_endpoints()` is a convenience
+    method for returning the destination of the associated CablePath, if any.
     """
+
     _path = models.ForeignKey(
         to='dcim.CablePath',
         on_delete=models.SET_NULL,
         null=True,
-        blank=True
+        blank=True,
     )
 
     class Meta:
@@ -323,39 +327,74 @@ class PathEndpoint(models.Model):
 
         # Construct the complete path (including e.g. bridged interfaces)
         while origin is not None:
-
-            if origin._path is None:
+            # Go through the public accessor rather than dereferencing `_path`
+            # directly. During cable edits, CablePath rows can be deleted and
+            # recreated while this endpoint instance is still in memory.
+            cable_path = origin.path
+            if cable_path is None:
                 break
 
-            path.extend(origin._path.path_objects)
+            path.extend(cable_path.path_objects)
 
-            # If the path ends at a non-connected pass-through port, pad out the link and far-end terminations
+            # If the path ends at a non-connected pass-through port, pad out
+            # the link and far-end terminations.
             if len(path) % 3 == 1:
                 path.extend(([], []))
-            # If the path ends at a site or provider network, inject a null "link" to render an attachment
+
+            # If the path ends at a site or provider network, inject a null
+            # "link" to render an attachment.
             elif len(path) % 3 == 2:
                 path.insert(-1, [])
 
-            # Check for a bridged relationship to continue the trace
-            destinations = origin._path.destinations
+            # Check for a bridged relationship to continue the trace.
+            destinations = cable_path.destinations
             if len(destinations) == 1:
                 origin = getattr(destinations[0], 'bridge', None)
             else:
                 origin = None
 
-        # Return the path as a list of three-tuples (A termination(s), cable(s), B termination(s))
+        # Return the path as a list of three-tuples
+        # (A termination(s), cable(s), B termination(s))
         return list(zip(*[iter(path)] * 3))
 
     @property
     def path(self):
-        return self._path
+        """
+        Return this endpoint's current CablePath, if any.
+
+        `_path` is a denormalized reference that is updated from CablePath
+        save/delete handlers, including queryset.update() calls on origin
+        endpoints. That means an already-instantiated endpoint can briefly hold
+        a stale in-memory `_path` relation while the database already points to
+        a different CablePath (or to no path at all).
+
+        If the cached relation points to a CablePath that has just been
+        deleted, refresh only the `_path` field from the database and retry.
+        This keeps the fix cheap and narrowly scoped to the denormalized FK.
+        """
+        if self._path_id is None:
+            return None
+
+        try:
+            return self._path
+        except ObjectDoesNotExist:
+            # Refresh only the denormalized FK instead of the whole model.
+            # The expected problem here is in-memory staleness during path
+            # rebuilds, not persistent database corruption.
+            self.refresh_from_db(fields=['_path'])
+            return self._path if self._path_id else None
 
     @cached_property
     def connected_endpoints(self):
         """
-        Caching accessor for the attached CablePath's destination (if any)
+        Caching accessor for the attached CablePath's destinations (if any).
+
+        Always route through `path` so stale in-memory `_path` references are
+        repaired before we cache the result for the lifetime of this instance.
         """
-        return self._path.destinations if self._path else []
+        if cable_path := self.path:
+            return cable_path.destinations
+        return []
 
 
 #

netbox/dcim/tests/test_models.py

@@ -5,6 +5,7 @@ from circuits.models import *
 from core.models import ObjectType
 from dcim.choices import *
 from dcim.models import *
+from extras.events import serialize_for_event
 from extras.models import CustomField
 from ipam.models import Prefix
 from netbox.choices import WeightUnitChoices
@@ -1274,6 +1275,65 @@ class CableTestCase(TestCase):
         self.assertEqual(a_terms, [interface1])
         self.assertEqual(b_terms, [interface2])
 
+    @tag('regression')  # #21498
+    def test_path_refreshes_replaced_cablepath_reference(self):
+        """
+        An already-instantiated interface should refresh its denormalized
+        `_path` foreign key when the referenced CablePath row has been
+        replaced in the database.
+        """
+        stale_interface = Interface.objects.get(device__name='TestDevice1', name='eth0')
+        old_path = CablePath.objects.get(pk=stale_interface._path_id)
+
+        new_path = CablePath(
+            path=old_path.path,
+            is_active=old_path.is_active,
+            is_complete=old_path.is_complete,
+            is_split=old_path.is_split,
+        )
+        old_path_id = old_path.pk
+        old_path.delete()
+        new_path.save()
+
+        # The old CablePath no longer exists
+        self.assertFalse(CablePath.objects.filter(pk=old_path_id).exists())
+
+        # The already-instantiated interface still points to the deleted path
+        # until the accessor refreshes `_path` from the database.
+        self.assertEqual(stale_interface._path_id, old_path_id)
+        self.assertEqual(stale_interface.path.pk, new_path.pk)
+
+    @tag('regression')  # #21498
+    def test_serialize_for_event_handles_stale_cablepath_reference_after_retermination(self):
+        """
+        Serializing an interface whose previously cached `_path` row has been
+        deleted during cable retermination must not raise.
+        """
+        stale_interface = Interface.objects.get(device__name='TestDevice2', name='eth0')
+        old_path_id = stale_interface._path_id
+        new_peer = Interface.objects.get(device__name='TestDevice2', name='eth1')
+        cable = stale_interface.cable
+
+        self.assertIsNotNone(cable)
+        self.assertIsNotNone(old_path_id)
+        self.assertEqual(stale_interface.cable_end, 'B')
+
+        cable.b_terminations = [new_peer]
+        cable.save()
+
+        # The old CablePath was deleted during retrace.
+        self.assertFalse(CablePath.objects.filter(pk=old_path_id).exists())
+
+        # The stale in-memory instance still holds the deleted FK value.
+        self.assertEqual(stale_interface._path_id, old_path_id)
+
+        # Serialization must not raise ObjectDoesNotExist. Because this interface
+        # was the former B-side termination, it is now disconnected.
+        data = serialize_for_event(stale_interface)
+        self.assertIsNone(data['connected_endpoints'])
+        self.assertIsNone(data['connected_endpoints_type'])
+        self.assertFalse(data['connected_endpoints_reachable'])
+
 
 class VirtualDeviceContextTestCase(TestCase):
 

netbox/extras/events.py

@@ -25,22 +25,59 @@ logger = logging.getLogger('netbox.events_processor')
 
 class EventContext(UserDict):
     """
-    A custom dictionary that automatically serializes its associated object on demand.
+    Dictionary-compatible wrapper for queued events that lazily serializes
+    ``event['data']`` on first access.
+
+    Backward-compatible with the plain-dict interface expected by existing
+    EVENTS_PIPELINE consumers. When the same object is enqueued more than once
+    in a single request, the serialization source is updated so consumers see
+    the latest state.
     """
 
-    # We're emulating a dictionary here (rather than using a custom class) because prior to NetBox v4.5.2, events were
-    # queued as dictionaries for processing by handles in EVENTS_PIPELINE. We need to avoid introducing any breaking
-    # changes until a suitable minor release.
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+
+        # Track which model instance should be serialized if/when `data` is
+        # requested. This may be refreshed on duplicate enqueue, while leaving
+        # the public `object` entry untouched for compatibility.
+        self._serialization_source = self.get('object')
+
+    def refresh_serialization_source(self, instance):
+        """
+        Point lazy serialization at a fresher instance, invalidating any
+        already-materialized ``data``.
+        """
+        self._serialization_source = instance
+        # UserDict.__contains__ checks the backing dict directly, so `in`
+        # does not trigger __getitem__'s lazy serialization.
+        if 'data' in self:
+            del self['data']
+
+    def freeze_data(self, instance):
+        """
+        Eagerly serialize and cache the payload for delete events, where the
+        object may become inaccessible after deletion.
+        """
+        super().__setitem__('data', serialize_for_event(instance))
+        self._serialization_source = None
+
     def __getitem__(self, item):
         if item == 'data' and 'data' not in self:
-            data = serialize_for_event(self['object'])
-            self.__setitem__('data', data)
+            # Materialize the payload only when an event consumer asks for it.
+            #
+            # On coalesced events, use the latest explicitly queued instance so
+            # webhooks/scripts/notifications observe the final queued state for
+            # that object within the request.
+            source = self._serialization_source or super().__getitem__('object')
+            super().__setitem__('data', serialize_for_event(source))
+
         return super().__getitem__(item)
 
 
 def serialize_for_event(instance):
     """
-    Return a serialized representation of the given instance suitable for use in a queued event.
+    Return a serialized representation of the given instance suitable for use
+    in a queued event.
     """
     serializer_class = get_serializer_for_model(instance.__class__)
     serializer_context = {
@@ -53,7 +90,8 @@ def serialize_for_event(instance):
 
 def get_snapshots(instance, event_type):
     """
-    Return a dictionary of pre- and post-change snapshots for the given instance.
+    Return a dictionary of pre- and post-change snapshots for the given
+    instance.
     """
     if event_type == OBJECT_DELETED:
         # Post-change snapshot must be empty for deleted objects
@@ -76,8 +114,9 @@ def get_snapshots(instance, event_type):
 
 def enqueue_event(queue, instance, request, event_type):
     """
-    Enqueue a serialized representation of a created/updated/deleted object for the processing of
-    events once the request has completed.
+    Enqueue (or coalesce) an event for a created/updated/deleted object.
+
+    Events are processed after the request completes.
     """
     # Bail if this type of object does not support event rules
     if not has_feature(instance, 'event_rules'):
@@ -88,11 +127,18 @@ def enqueue_event(queue, instance, request, event_type):
 
     assert instance.pk is not None
     key = f'{app_label}.{model_name}:{instance.pk}'
+
     if key in queue:
         queue[key]['snapshots']['postchange'] = get_snapshots(instance, event_type)['postchange']
-        # If the object is being deleted, update any prior "update" event to "delete"
+
+        # If the object is being deleted, convert any prior update event into a
+        # delete event and freeze the payload before the object (or related
+        # rows) become inaccessible.
         if event_type == OBJECT_DELETED:
             queue[key]['event_type'] = event_type
+        else:
+            # Keep the public `object` entry stable for compatibility.
+            queue[key].refresh_serialization_source(instance)
     else:
         queue[key] = EventContext(
             object_type=ObjectType.objects.get_for_model(instance),
@@ -106,14 +152,16 @@ def enqueue_event(queue, instance, request, event_type):
             username=request.user.username,  # DEPRECATED, will be removed in NetBox v4.7.0
             request_id=request.id,           # DEPRECATED, will be removed in NetBox v4.7.0
         )
-    # Force serialization of objects prior to them actually being deleted
+
+    # For delete events, eagerly serialize the payload before the row is gone.
+    # This covers both first-time enqueues and coalesced update→delete promotions.
     if event_type == OBJECT_DELETED:
-        queue[key]['data'] = serialize_for_event(instance)
+        queue[key].freeze_data(instance)
 
 
 def process_event_rules(event_rules, object_type, event):
     """
-    Process a list of EventRules against an event.
+    Evaluate and dispatch a list of EventRules against an event.
 
     Notes on event sources:
     - Object change events (created/updated/deleted) are enqueued via
@@ -133,9 +181,9 @@ def process_event_rules(event_rules, object_type, event):
         if not event_rule.eval_conditions(event['data']):
             continue
 
-        # Compile event data
-        event_data = event_rule.action_data or {}
-        event_data.update(event['data'])
+        # Merge rule-specific action_data with the event payload.
+        # Copy to avoid mutating the rule's stored action_data dict.
+        event_data = {**(event_rule.action_data or {}), **event['data']}
 
         # Webhooks
         if event_rule.action_type == EventRuleActionChoices.WEBHOOK:

netbox/extras/tests/test_event_rules.py

@@ -1,8 +1,10 @@
 import json
 import uuid
+from unittest import skipIf
 from unittest.mock import Mock, patch
 
 import django_rq
+from django.conf import settings
 from django.http import HttpResponse
 from django.test import RequestFactory
 from django.urls import reverse
@@ -343,6 +345,7 @@ class EventRuleTest(APITestCase):
             self.assertEqual(job.kwargs['snapshots']['prechange']['name'], sites[i].name)
             self.assertEqual(job.kwargs['snapshots']['prechange']['tags'], ['Bar', 'Foo'])
 
+    @skipIf('netbox.tests.dummy_plugin' not in settings.PLUGINS, 'dummy_plugin not in settings.PLUGINS')
     def test_send_webhook(self):
         request_id = uuid.uuid4()
 
@@ -426,6 +429,97 @@ class EventRuleTest(APITestCase):
         self.assertEqual(job.kwargs['object_type'], script_type)
         self.assertEqual(job.kwargs['username'], self.user.username)
 
+    def test_duplicate_enqueue_refreshes_lazy_payload(self):
+        """
+        When the same object is enqueued more than once in a single request,
+        lazy serialization should use the most recently enqueued instance while
+        preserving the original event['object'] reference.
+        """
+        request = RequestFactory().get(reverse('dcim:site_add'))
+        request.id = uuid.uuid4()
+        request.user = self.user
+
+        site = Site.objects.create(name='Site 1', slug='site-1')
+        stale_site = Site.objects.get(pk=site.pk)
+
+        queue = {}
+        enqueue_event(queue, stale_site, request, OBJECT_UPDATED)
+
+        event = queue[f'dcim.site:{site.pk}']
+
+        # Data should not be materialized yet (lazy serialization)
+        self.assertNotIn('data', event.data)
+
+        fresh_site = Site.objects.get(pk=site.pk)
+        fresh_site.description = 'foo'
+        fresh_site.save()
+
+        enqueue_event(queue, fresh_site, request, OBJECT_UPDATED)
+
+        # The original object reference should be preserved
+        self.assertIs(event['object'], stale_site)
+
+        # But serialized data should reflect the fresher instance
+        self.assertEqual(event['data']['description'], 'foo')
+        self.assertEqual(event['snapshots']['postchange']['description'], 'foo')
+
+    def test_duplicate_enqueue_invalidates_materialized_data(self):
+        """
+        If event['data'] has already been materialized before a second enqueue
+        for the same object, the stale payload should be discarded and rebuilt
+        from the fresher instance on next access.
+        """
+        request = RequestFactory().get(reverse('dcim:site_add'))
+        request.id = uuid.uuid4()
+        request.user = self.user
+
+        site = Site.objects.create(name='Site 1', slug='site-1')
+
+        queue = {}
+        enqueue_event(queue, site, request, OBJECT_UPDATED)
+
+        event = queue[f'dcim.site:{site.pk}']
+
+        # Force early materialization
+        self.assertEqual(event['data']['description'], '')
+
+        # Now update and re-enqueue
+        fresh_site = Site.objects.get(pk=site.pk)
+        fresh_site.description = 'updated'
+        fresh_site.save()
+
+        enqueue_event(queue, fresh_site, request, OBJECT_UPDATED)
+
+        # Stale data should have been invalidated; new access should reflect update
+        self.assertEqual(event['data']['description'], 'updated')
+
+    def test_update_then_delete_enqueue_freezes_payload(self):
+        """
+        When an update event is coalesced with a subsequent delete, the event
+        type should be promoted to OBJECT_DELETED and the payload should be
+        eagerly frozen (since the object will be inaccessible after deletion).
+        """
+        request = RequestFactory().get(reverse('dcim:site_add'))
+        request.id = uuid.uuid4()
+        request.user = self.user
+
+        site = Site.objects.create(name='Site 1', slug='site-1')
+
+        queue = {}
+        enqueue_event(queue, site, request, OBJECT_UPDATED)
+
+        event = queue[f'dcim.site:{site.pk}']
+
+        enqueue_event(queue, site, request, OBJECT_DELETED)
+
+        # Event type should have been promoted
+        self.assertEqual(event['event_type'], OBJECT_DELETED)
+
+        # Data should already be materialized (frozen), not lazy
+        self.assertIn('data', event.data)
+        self.assertEqual(event['data']['name'], 'Site 1')
+        self.assertIsNone(event['snapshots']['postchange'])
+
     def test_duplicate_triggers(self):
         """
         Test for erroneous duplicate event triggers resulting from saving an object multiple times