6347 Cache the number of each component type assigned to devices/VMs (#12632)

---------

Co-authored-by: Jeremy Stretch <jstretch@netboxlabs.com>

netbox/utilities/tests/test_counters.py

@@ -0,0 +1,69 @@
+from django.test import TestCase
+
+from dcim.models import *
+from utilities.testing.utils import create_test_device
+
+
+class CountersTest(TestCase):
+    """
+    Validate the operation of dict_to_filter_params().
+    """
+    @classmethod
+    def setUpTestData(cls):
+
+        # Create devices
+        device1 = create_test_device('Device 1')
+        device2 = create_test_device('Device 2')
+
+        # Create interfaces
+        Interface.objects.create(device=device1, name='Interface 1')
+        Interface.objects.create(device=device1, name='Interface 2')
+        Interface.objects.create(device=device2, name='Interface 3')
+        Interface.objects.create(device=device2, name='Interface 4')
+
+    def test_interface_count_creation(self):
+        """
+        When a tracked object (Interface) is added the tracking counter should be updated.
+        """
+        device1, device2 = Device.objects.all()
+        self.assertEqual(device1.interface_count, 2)
+        self.assertEqual(device2.interface_count, 2)
+
+        Interface.objects.create(device=device1, name='Interface 5')
+        Interface.objects.create(device=device2, name='Interface 6')
+        device1.refresh_from_db()
+        device2.refresh_from_db()
+        self.assertEqual(device1.interface_count, 3)
+        self.assertEqual(device2.interface_count, 3)
+
+    def test_interface_count_deletion(self):
+        """
+        When a tracked object (Interface) is deleted the tracking counter should be updated.
+        """
+        device1, device2 = Device.objects.all()
+        self.assertEqual(device1.interface_count, 2)
+        self.assertEqual(device2.interface_count, 2)
+
+        Interface.objects.get(name='Interface 1').delete()
+        Interface.objects.get(name='Interface 3').delete()
+        device1.refresh_from_db()
+        device2.refresh_from_db()
+        self.assertEqual(device1.interface_count, 1)
+        self.assertEqual(device2.interface_count, 1)
+
+    def test_interface_count_move(self):
+        """
+        When a tracked object (Interface) is moved the tracking counter should be updated.
+        """
+        device1, device2 = Device.objects.all()
+        self.assertEqual(device1.interface_count, 2)
+        self.assertEqual(device2.interface_count, 2)
+
+        interface1 = Interface.objects.get(name='Interface 1')
+        interface1.device = device2
+        interface1.save()
+
+        device1.refresh_from_db()
+        device2.refresh_from_db()
+        self.assertEqual(device1.interface_count, 1)
+        self.assertEqual(device2.interface_count, 3)