Recruit existing DNS record when adding coupled IP address

When an IP address is created, and the DNS coupling is requested, if
the given name and zone match an existing and unmanaged DNS record,
the record is linked to the IP address and becomes managed.

0) DNS Record "R" pre-exists and has the following characteristics:
   id=1, name=foo, zone=example.com, type=A, value=10.0.0.1, managed=False

1) IP address, with address=10.0.0.1/24, cf_name=foo, cf_zone=example.com
   is requested for creation.

2) The IP address is created and points to the DNS record "R":
   address=10.0.0.1/24, cf_dns_record=1 ...

3) The DNS Record R becomes managed:
   id=1, ... , managed=True

netbox_dns/middleware.py

@@ -91,22 +91,32 @@ def post_save(self, sender, **kwargs):
                 ip.dns_name = f"{name}.{zone.name}"
                 ip.save(update_fields=["dns_name"])
 
-            # create DNS record
             else:
-                record = Record(
-                    name=name,
-                    zone=zone,
-                    type=RecordTypeChoices.AAAA
-                    if ip.family == 6
-                    else RecordTypeChoices.A,
-                    value=str(ip.address.ip),
-                    managed=True,
-                )
+                # Fetch an existing (unmanaged) DNS record or create a new one
+                type = (RecordTypeChoices.AAAA if ip.family == 6 else RecordTypeChoices.A)
+                value = str(ip.address.ip)
+                try:
+                    record = Record.objects.get(
+                        name=name,
+                        zone=zone,
+                        value=value,
+                        type=type,
+                        managed=False
+                    )
+                    record.managed = True
+                except:
+                    record = Record(
+                        name=name,
+                        zone=zone,
+                        type=type,
+                        value=value,
+                        managed=True,
+                    )
 
                 check_record_permission(
                     user, record, "netbox_dns.add_record", commit=True
                 )
-                # link record to IP Address
+                # Link record to IP Address
                 ip.custom_field_data["dns_record"] = record.id
                 # cosmetic: update dns_name field with FQDN
                 ip.dns_name = f"{name}.{zone.name}"
@@ -145,6 +155,7 @@ def check_record_permission(user, record, perm, commit=False):
         with transaction.atomic():
             # Save record when adding
             # Rollback is done at the end of the transaction, unless committed
+
             if action == "add":
                 record.save()
 

netbox_dns/tests/coupling/test_ip_dns_coupling.py

@@ -64,6 +64,37 @@ def test_create_ip(self):
         ipaddress = IPAddress.objects.get(id=response.data["id"])
         self.assertEqual(ipaddress.dns_name, f"{name}.{zone.name}")
 
+    @override_settings(PLUGINS_CONFIG={"netbox_dns": {"feature_ipam_coupling": True}})
+    def test_create_ip_existing_dns_record(self):
+        zone = self.zone
+        name = "test-create-ip-existing-dns-record"
+        addr = "10.0.0.25/24"
+
+        # Create DNS record
+        A = RecordTypeChoices.A
+        v = str(IPNetwork(addr).ip)
+        record = Record.objects.create(name=name, zone=zone, type=A, value=v)
+
+        # Grant permissions to user
+        self.add_permissions("ipam.add_ipaddress")
+        self.add_permissions("netbox_dns.add_record")
+
+        url = reverse("ipam-api:ipaddress-list")
+        data = {"address": addr, "custom_fields": {"zone": zone.id, "name": name}}
+        response = self.client.post(url, data, format="json", **self.header)
+
+        self.assertTrue(status.is_success(response.status_code))
+
+        # Check if "record" has been linked to and is now managed
+        record_id = response.data["custom_fields"]["dns_record"]["id"]
+        self.assertEqual(record_id, record.id)
+        record = Record.objects.get(id=record.id)
+        self.assertTrue(record.managed)
+        # Check value of dns_name
+        ipaddress = IPAddress.objects.get(id=response.data["id"])
+        self.assertEqual(ipaddress.dns_name, f"{name}.{zone.name}")
+
+
     @override_settings(PLUGINS_CONFIG={"netbox_dns": {"feature_ipam_coupling": True}})
     def test_create_ip_missing_dns_permission(self):
         zone = self.zone