Fixes #2683: Fix exception when connecting a cable to a RearPort with no corresponding FrontPort

CHANGELOG.md

@@ -12,6 +12,7 @@ v2.5.1 (FUTURE)
 * [#2676](https://github.com/digitalocean/netbox/issues/2676) - Fix exception when passing dictionary value to a ChoiceField
 * [#2678](https://github.com/digitalocean/netbox/issues/2678) - Fix error when viewing webhook in admin UI without write permission
 * [#2680](https://github.com/digitalocean/netbox/issues/2680) - Disallow POST requests to `/dcim/interface-connections/` API endpoint
+* [#2683](https://github.com/digitalocean/netbox/issues/2683) - Fix exception when connecting a cable to a RearPort with no corresponding FrontPort
 * [#2684](https://github.com/digitalocean/netbox/issues/2684) - Fix custom field filtering
 
 ---

netbox/dcim/models.py

@@ -110,11 +110,14 @@ class CableTermination(models.Model):
                     raise Exception("Invalid position for {} ({} positions): {})".format(
                         termination, termination.positions, position
                     ))
-                peer_port = FrontPort.objects.get(
+                try:
-                    rear_port=termination,
+                    peer_port = FrontPort.objects.get(
-                    rear_port_position=position,
+                        rear_port=termination,
-                )
+                        rear_port_position=position,
-                return peer_port, 1
+                    )
+                    return peer_port, 1
+                except ObjectDoesNotExist:
+                    return None, None
 
             # Follow a circuit to its other termination
             elif isinstance(termination, CircuitTermination) and follow_circuits:
@@ -2629,5 +2632,7 @@ class Cable(ChangeLoggedModel):
                     path_status = CONNECTION_STATUS_PLANNED
                     break
 
-        # (A path end, B path end, connected/planned)
+        a_endpoint = a_path[-1][2]
-        return a_path[-1][2], b_path[-1][2], path_status
+        b_endpoint = b_path[-1][2]
+
+        return a_endpoint, b_endpoint, path_status

netbox/dcim/signals.py

@@ -37,7 +37,7 @@ def update_connected_endpoints(instance, **kwargs):
 
     # Check if this Cable has formed a complete path. If so, update both endpoints.
     endpoint_a, endpoint_b, path_status = instance.get_path_endpoints()
-    if endpoint_a is not None and endpoint_b is not None:
+    if hasattr(endpoint_a, 'connected_endpoint') and hasattr(endpoint_b, 'connected_endpoint'):
         endpoint_a.connected_endpoint = endpoint_b
         endpoint_a.connection_status = path_status
         endpoint_a.save()
@@ -62,7 +62,7 @@ def nullify_connected_endpoints(instance, **kwargs):
         instance.termination_b.save()
 
     # If this Cable was part of a complete path, tear it down
-    if endpoint_a is not None and endpoint_b is not None:
+    if hasattr(endpoint_a, 'connected_endpoint') and hasattr(endpoint_b, 'connected_endpoint'):
         endpoint_a.connected_endpoint = None
         endpoint_a.connection_status = None
         endpoint_a.save()