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

---------

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

netbox/utilities/fields.py

@@ -2,6 +2,7 @@ from collections import defaultdict
 
 from django.contrib.contenttypes.fields import GenericForeignKey
 from django.db import models
+from django.utils.translation import gettext_lazy as _
 
 from utilities.ordering import naturalize
 from .forms.widgets import ColorSelect
@@ -9,6 +10,7 @@ from .validators import ColorValidator
 
 __all__ = (
     'ColorField',
+    'CounterCacheField',
     'NaturalOrderingField',
     'NullableCharField',
     'RestrictedGenericForeignKey',
@@ -143,3 +145,43 @@ class RestrictedGenericForeignKey(GenericForeignKey):
             self.name,
             False,
         )
+
+
+class CounterCacheField(models.BigIntegerField):
+    """
+    Counter field to keep track of related model counts.
+    """
+    def __init__(self, to_model, to_field, *args, **kwargs):
+        if not isinstance(to_model, str):
+            raise TypeError(
+                _("%s(%r) is invalid. to_model parameter to CounterCacheField must be "
+                  "a string in the format 'app.model'")
+                % (
+                    self.__class__.__name__,
+                    to_model,
+                )
+            )
+
+        if not isinstance(to_field, str):
+            raise TypeError(
+                _("%s(%r) is invalid. to_field parameter to CounterCacheField must be "
+                  "a string in the format 'field'")
+                % (
+                    self.__class__.__name__,
+                    to_field,
+                )
+            )
+
+        self.to_model_name = to_model
+        self.to_field_name = to_field
+
+        kwargs['default'] = kwargs.get('default', 0)
+        kwargs['editable'] = False
+
+        super().__init__(*args, **kwargs)
+
+    def deconstruct(self):
+        name, path, args, kwargs = super().deconstruct()
+        kwargs["to_model"] = self.to_model_name
+        kwargs["to_field"] = self.to_field_name
+        return name, path, args, kwargs