Fixes #18991: AttributeError: NoneType object has not attribute model

`GenericArrayForeignKey`, which was added in #18826, advertised itself
as a many_to_many relation, which is somewhat inaccurate and triggered
DRF's introspection of many_to_many relations which looks for a
`remote_field.model` property chain on the relation. Since that doesn't
exist, DRF threw an AttributeError resulting in a 500 error.

This changes `GenericArrayForeignKey` to advertise itself to DRF as a
one_to_many relation, which is more accurate, and does not trigger the
property access in DRF that was causing the problem.

This also adds a regression test for both FrontPort and RearPort "path"
API view.

netbox/dcim/tests/test_api.py

@@ -1,6 +1,6 @@
 import json
 
-from django.test import override_settings
+from django.test import override_settings, tag
 from django.urls import reverse
 from django.utils.translation import gettext as _
 from rest_framework import status
@@ -1904,6 +1904,27 @@ class FrontPortTest(APIViewTestCases.APIViewTestCase):
             },
         ]
 
+    @tag('regression')  # Issue #18991
+    def test_front_port_paths(self):
+        device = Device.objects.first()
+        rear_port = RearPort.objects.create(
+            device=device, name='Rear Port 10', type=PortTypeChoices.TYPE_8P8C
+        )
+        interface1 = Interface.objects.create(device=device, name='Interface 1')
+        front_port = FrontPort.objects.create(
+            device=device,
+            name='Rear Port 10',
+            type=PortTypeChoices.TYPE_8P8C,
+            rear_port=rear_port,
+        )
+        Cable.objects.create(a_terminations=[interface1], b_terminations=[front_port])
+
+        self.add_permissions(f'dcim.view_{self.model._meta.model_name}')
+        url = reverse(f'dcim-api:{self.model._meta.model_name}-paths', kwargs={'pk': front_port.pk})
+        response = self.client.get(url, **self.header)
+
+        self.assertHttpStatus(response, status.HTTP_200_OK)
+
 
 class RearPortTest(APIViewTestCases.APIViewTestCase):
     model = RearPort
@@ -1947,6 +1968,23 @@ class RearPortTest(APIViewTestCases.APIViewTestCase):
             },
         ]
 
+    @tag('regression')  # Issue #18991
+    def test_rear_port_paths(self):
+        device = Device.objects.first()
+        interface1 = Interface.objects.create(device=device, name='Interface 1')
+        rear_port = RearPort.objects.create(
+            device=device,
+            name='Rear Port 10',
+            type=PortTypeChoices.TYPE_8P8C,
+        )
+        Cable.objects.create(a_terminations=[interface1], b_terminations=[rear_port])
+
+        self.add_permissions(f'dcim.view_{self.model._meta.model_name}')
+        url = reverse(f'dcim-api:{self.model._meta.model_name}-paths', kwargs={'pk': rear_port.pk})
+        response = self.client.get(url, **self.header)
+
+        self.assertHttpStatus(response, status.HTTP_200_OK)
+
 
 class ModuleBayTest(APIViewTestCases.APIViewTestCase):
     model = ModuleBay

netbox/utilities/fields.py

@@ -198,9 +198,9 @@ class GenericArrayForeignKey(FieldCacheMixin, models.Field):
     Provide a generic many-to-many relation through an 2d array field
     """
 
-    many_to_many = True
+    many_to_many = False
     many_to_one = False
-    one_to_many = False
+    one_to_many = True
     one_to_one = False
 
     def __init__(self, field, for_concrete_model=True):