feat(dcim): Add device, module and rack count filters

Introduces `device_count`, `module_count` and `rack_count` filters to
enable queries based on the existence and count of the associated
device, module or rack instances.
Updates forms, filtersets, and GraphQL schema to support these filters,
along with tests for validation.

Fixes #19523

netbox/dcim/api/serializers_/devicetypes.py

@@ -5,7 +5,7 @@ from rest_framework import serializers
 
 from dcim.choices import *
 from dcim.models import DeviceType, ModuleType, ModuleTypeProfile
-from netbox.api.fields import AttributesField, ChoiceField, RelatedObjectCountField
+from netbox.api.fields import AttributesField, ChoiceField
 from netbox.api.serializers import PrimaryModelSerializer
 from netbox.choices import *
 from .manufacturers import ManufacturerSerializer
@@ -45,9 +45,7 @@ class DeviceTypeSerializer(PrimaryModelSerializer):
     device_bay_template_count = serializers.IntegerField(read_only=True)
     module_bay_template_count = serializers.IntegerField(read_only=True)
     inventory_item_template_count = serializers.IntegerField(read_only=True)
-
-    # Related object counts
-    device_count = RelatedObjectCountField('instances')
+    device_count = serializers.IntegerField(read_only=True)
 
     class Meta:
         model = DeviceType
@@ -100,12 +98,13 @@ class ModuleTypeSerializer(PrimaryModelSerializer):
         required=False,
         allow_null=True
     )
+    module_count = serializers.IntegerField(read_only=True)
 
     class Meta:
         model = ModuleType
         fields = [
             'id', 'url', 'display_url', 'display', 'profile', 'manufacturer', 'model', 'part_number', 'airflow',
             'weight', 'weight_unit', 'description', 'attributes', 'owner', 'comments', 'tags', 'custom_fields',
-            'created', 'last_updated',
+            'created', 'last_updated', 'module_count',
         ]
-        brief_fields = ('id', 'url', 'display', 'profile', 'manufacturer', 'model', 'description')
+        brief_fields = ('id', 'url', 'display', 'profile', 'manufacturer', 'model', 'description', 'module_count')

netbox/dcim/api/serializers_/racks.py

@@ -62,9 +62,8 @@ class RackBaseSerializer(PrimaryModelSerializer):
 
 
 class RackTypeSerializer(RackBaseSerializer):
-    manufacturer = ManufacturerSerializer(
-        nested=True
-    )
+    manufacturer = ManufacturerSerializer(nested=True)
+    rack_count = serializers.IntegerField(read_only=True)
 
     class Meta:
         model = RackType
@@ -72,9 +71,9 @@ class RackTypeSerializer(RackBaseSerializer):
             'id', 'url', 'display_url', 'display', 'manufacturer', 'model', 'slug', 'description', 'form_factor',
             'width', 'u_height', 'starting_unit', 'desc_units', 'outer_width', 'outer_height', 'outer_depth',
             'outer_unit', 'weight', 'max_weight', 'weight_unit', 'mounting_depth', 'description', 'owner', 'comments',
-            'tags', 'custom_fields', 'created', 'last_updated',
+            'tags', 'custom_fields', 'created', 'last_updated', 'rack_count',
         ]
-        brief_fields = ('id', 'url', 'display', 'manufacturer', 'model', 'slug', 'description')
+        brief_fields = ('id', 'url', 'display', 'manufacturer', 'model', 'slug', 'description', 'rack_count')
 
 
 class RackSerializer(RackBaseSerializer):