Fixes #21045: Allow saving Site with associated Prefix

This was a result of the fix for #20944 optimizing a query to only
include the `id` field with `.only(id)`. Since `Prefix.__init__()`
caches original values from other fields (`_prefix` and `_vrf_id`),
these cached values are `None` at init-time.

This might not normally be a problem, but the sequence of events in
the bug report also end up causing the `handle_prefix_saved` handler
to run, which uses an ORM lookup, (either `net_contained_or_equal`
original`net_contained`) that does not support a query argument of
`None`.

netbox/dcim/signals.py

@@ -210,7 +210,7 @@ def sync_cached_scope_fields(instance, created, **kwargs):
     for model in (Prefix, Cluster, WirelessLAN):
         qs = model.objects.filter(**filters)
 
-        for obj in qs.only('id'):
+        for obj in qs:
             # Recompute cache using the same logic as save()
             obj.cache_related_objects()
             obj.save(update_fields=[

netbox/dcim/tests/test_models.py

@@ -6,6 +6,7 @@ from core.models import ObjectType
 from dcim.choices import *
 from dcim.models import *
 from extras.models import CustomField
+from ipam.models import Prefix
 from netbox.choices import WeightUnitChoices
 from tenancy.models import Tenant
 from utilities.data import drange
@@ -1192,3 +1193,14 @@ class VirtualChassisTestCase(TestCase):
         device2.vc_position = 1
         with self.assertRaises(ValidationError):
             device2.full_clean()
+
+
+class SiteSignalTestCase(TestCase):
+
+    @tag('regression')
+    def test_edit_site_with_prefix_no_vrf(self):
+        site = Site.objects.create(name='Test Site', slug='test-site')
+        Prefix.objects.create(prefix='192.0.2.0/24', scope=site, vrf=None)
+
+        # Regression test for #21045: should not raise ValueError
+        site.save()