Closes #20808: Show occupying Device in Rack Position Selector (#21744)

Add a description field to the rack unit serializer containing the
occupying Device, allowing the Rack position dropdown to show Device
context while keeping the existing display value unchanged.

Co-authored-by: Martin Hauser <mhauser@netboxlabs.com>

netbox/dcim/api/serializers_/rackunits.py

@@ -26,7 +26,12 @@ class RackUnitSerializer(serializers.Serializer):
     device = DeviceSerializer(nested=True, read_only=True)
     occupied = serializers.BooleanField(read_only=True)
     display = serializers.SerializerMethodField(read_only=True)
+    description = serializers.SerializerMethodField(read_only=True)
 
     @extend_schema_field(OpenApiTypes.STR)
     def get_display(self, obj):
         return obj['name']
+
+    @extend_schema_field(OpenApiTypes.STR)
+    def get_description(self, obj):
+        return f'{obj["device"]}' if obj['device'] else None

netbox/dcim/tests/test_api.py

@@ -716,6 +716,34 @@ class RackTestCase(APIViewTestCases.APIViewTestCase):
         response = self.client.get(f'{url}?q=U10', **self.header)
         self.assertEqual(response.data['count'], 2)
 
+    def test_get_rack_elevation_description_is_occupying_device_name(self):
+        """
+        Verify occupied rack units include the occupying device in their description.
+        """
+        rack = Rack.objects.first()
+        self.add_permissions('dcim.view_rack', 'dcim.view_device')
+        url = reverse('dcim-api:rack-elevation', kwargs={'pk': rack.pk})
+
+        device = create_test_device(
+            name='Device A',
+            site=rack.site,
+            rack=rack,
+            position=40,
+            face=DeviceFaceChoices.FACE_FRONT,
+        )
+
+        # Retrieve all units
+        response = self.client.get(url, **self.header)
+        self.assertHttpStatus(response, status.HTTP_200_OK)
+
+        occupied_unit = next(unit for unit in response.data['results'] if unit['name'] == 'U40')
+        self.assertEqual(occupied_unit['device']['id'], device.pk)
+        self.assertEqual(occupied_unit['description'], f'{device}')
+
+        unoccupied_unit = next(unit for unit in response.data['results'] if unit['name'] == 'U39')
+        self.assertEqual(unoccupied_unit['device'], None)
+        self.assertEqual(unoccupied_unit['description'], None)
+
     def test_get_rack_elevation_svg(self):
         """
         GET a single rack elevation in SVG format.