Do not clear DNS name if no coupled DNS record has been set

netbox_dns/signals/ipam_coupling.py

@@ -121,15 +121,27 @@ def ip_address_update_dns_information(instance, **kwargs):
 
     name, ttl, disable_ptr, zone_id = ipaddress_cf_data(instance)
 
+    previous_zone_id = None
+    if instance.pk is not None:
+        try:
+            old_instance = IPAddress.objects.get(pk=instance.pk)
+            previous_zone_id = old_instance.custom_field_data.get(
+                "ipaddress_dns_zone_id"
+            )
+        except IPAddress.DoesNotExist:
+            pass
+
     if zone_id is not None:
         instance.dns_name = f"{name}.{Zone.objects.get(pk=zone_id).name}"
     else:
-        instance.dns_name = ""
         instance.custom_field_data["ipaddress_dns_record_name"] = None
         instance.custom_field_data["ipaddress_dns_record_ttl"] = None
         instance.custom_field_data["ipaddress_dns_record_disable_ptr"] = False
         instance.custom_field_data["ipaddress_dns_zone_id"] = None
 
+        if previous_zone_id is not None:
+            instance.dns_name = ""
+
 
 #
 # Handle DNS record operation after IPAddress has been created or modified

netbox_dns/tests/ipam_coupling/test_records.py

@@ -607,3 +607,22 @@ def test_clear_disable_ptr_cf(self):
                 "ipaddress_dns_record_disable_ptr": False,
             },
         )
+
+    @override_settings(PLUGINS_CONFIG={"netbox_dns": {"feature_ipam_coupling": True}})
+    def test_dont_clear_existing_dns_name(self):
+        address = IPNetwork("10.0.0.27/24")
+        dns_name = "test.example.com"
+
+        ip_address = IPAddress.objects.create(
+            address=address,
+            dns_name=dns_name,
+            custom_field_data={
+                "ipaddress_dns_zone_id": None,
+                "ipaddress_dns_record_name": None,
+                "ipaddress_dns_record_ttl": None,
+                "ipaddress_dns_record_disable_ptr": True,
+            },
+        )
+        record_query = Record.objects.filter(ipam_ip_address=ip_address)
+        self.assertFalse(record_query.exists())
+        self.assertEqual(ip_address.dns_name, dns_name)