[fix] Fixed "receive_url" field in TopologyAdmin

README.rst

@@ -295,6 +295,8 @@ Sending data for topology with RECEIVE strategy
 
    E.g., in our case the URL is ``http://127.0.0.1:8000/api/v1/network-topology/topology/d17e539a-1793-4be2-80a4-c305eca64fd8/receive/?key=cMGsvio8q0L0BGLd5twiFHQOqIEKI423``.
 
+   **Note:** The topology receive URL is shown only after the topology object is created.
+
 2. Create a script (eg: ``/opt/send-topology.sh``) which sends the topology
    data using ``POST``, in the example script below we are sending the
    status log data of OpenVPN but the same code can be applied to other

openwisp_network_topology/admin.py

@@ -104,6 +104,14 @@ class TopologyAdmin(
     receive_url_baseurl = app_settings.TOPOLOGY_API_BASEURL
     change_form_template = 'admin/topology/topology/change_form.html'
 
+    def get_fields(self, request, obj=None):
+        fields = list(super().get_fields(request, obj))
+        if not obj:
+            # Receive URL cannot be created without an object.
+            # Hence, remove the "receive_url" field.
+            fields.remove('receive_url')
+        return fields
+
     def get_actions(self, request):
         """
         move delete action to last position

openwisp_network_topology/integrations/device/tests/test_wifi_mesh.py

@@ -266,8 +266,14 @@ def test_topology_admin(self):
         """
         admin = self._create_admin()
         self.client.force_login(admin)
-        topology = self._create_topology()
-        response = self.client.get(
-            reverse(f'{self.prefix}_topology_change', args=[topology.id])
-        )
-        self.assertContains(response, 'Wifi mesh')
+
+        with self.subTest('Test add form'):
+            response = self.client.get(reverse(f'{self.prefix}_topology_add'))
+            self.assertContains(response, 'Wifi mesh')
+
+        with self.subTest('Test change form'):
+            topology = self._create_topology()
+            response = self.client.get(
+                reverse(f'{self.prefix}_topology_change', args=[topology.id])
+            )
+            self.assertContains(response, 'Wifi mesh')