Fixes: #18263 - Iterate through a freshly queried set of CableTerminations to find endpoints in update_connected_endpoints

[bctiemann]

Fixes: #18263

During an API PATCH update to a Cable where one or both endpoints is changed, the signal handler update_connected_endpoints iterates through self.terminations.all() which in the case of an API call has not necessarily been refreshed after the deletion of stale endpoints at

netbox/netbox/dcim/models/cables.py

Lines 224 to 240 in b6265d8

	# Delete stale CableTerminations
	if self._terminations_modified:
	for termination, ct in a_terminations.items():
	if termination.pk and termination not in self.a_terminations:
	ct.delete()
	for termination, ct in b_terminations.items():
	if termination.pk and termination not in self.b_terminations:
	ct.delete()
	# Save new CableTerminations (if any)
	if self._terminations_modified:
	for termination in self.a_terminations:
	if not termination.pk or termination not in a_terminations:
	CableTermination(cable=self, cable_end='A', termination=termination).save()
	for termination in self.b_terminations:
	if not termination.pk or termination not in b_terminations:
	CableTermination(cable=self, cable_end='B', termination=termination).save()

This leads to the local_cable_terminations being empty here (because the pks don't match):

netbox/netbox/dcim/models/cables.py

Lines 597 to 611 in b6265d8

	# Step 6: Determine the far-end terminations
	if isinstance(links[0], Cable):
	termination_type = ObjectType.objects.get_for_model(terminations[0])
	local_cable_terminations = CableTermination.objects.filter(
	termination_type=termination_type,
	termination_id__in=[t.pk for t in terminations]
	)
	q_filter = Q()
	for lct in local_cable_terminations:
	cable_end = 'A' if lct.cable_end == 'B' else 'B'
	q_filter |= Q(cable=lct.cable, cable_end=cable_end)
	remote_cable_terminations = CableTermination.objects.filter(q_filter)
	remote_terminations = [ct.termination for ct in remote_cable_terminations]

(Step 6 of Cable.from_origin), which leads to q_filter being empty and thus the completely unfiltered iteration at L611 potentially taking O(n) time depending on the number of terminations in the DB.

This change ensures that the iteration of CableTerminations associated with a Cable after an update is freshly queried from the DB following the deletion of stale endpoints rather than relying on the (potentially stale or cached) self.terminations reverse relation, and thus ensuring from_origin is calculated correctly.