Closes #15087: Support for specifying a subset of API serializer fields (#15122)

* Enable dynamic field inclusion for REST API serializers

* Recurse through nested serializer when resolving prefetches

* Remove obsolete calls to prefetch_related() for API views

* Remove support for brief_prefetch_fields viewset attribute

* Rename query parameter

* Fixes #15133: Fix FHRP group representation on assignments endpoint under brief mode (#15134)

* Fixes #15133: Fix FHRP group representation on assignments endpoint under brief mode

* Update API test

* Restore get_queryset() on BriefModeMixin, minus prefetch logic

* get_prefetches_for_serializer() should reference serializer field source if set

netbox/utilities/api.py

@@ -2,9 +2,13 @@ import platform
 import sys
 
 from django.conf import settings
+from django.contrib.contenttypes.fields import GenericForeignKey
+from django.core.exceptions import FieldDoesNotExist
+from django.db.models.fields.related import ManyToOneRel, RelatedField
 from django.http import JsonResponse
 from django.urls import reverse
 from rest_framework import status
+from rest_framework.serializers import Serializer
 from rest_framework.utils import formatting
 
 from netbox.api.exceptions import GraphQLTypeNotFound, SerializerNotFound
@@ -12,6 +16,7 @@ from .utils import dynamic_import
 
 __all__ = (
     'get_graphql_type_for_model',
+    'get_prefetches_for_serializer',
     'get_serializer_for_model',
     'get_view_name',
     'is_api_request',
@@ -89,6 +94,43 @@ def get_view_name(view, suffix=None):
     return name
 
 
+def get_prefetches_for_serializer(serializer_class, fields_to_include=None):
+    """
+    Compile and return a list of fields which should be prefetched on the queryset for a serializer.
+    """
+    model = serializer_class.Meta.model
+
+    # If specific fields are not specified, default to all
+    if not fields_to_include:
+        fields_to_include = serializer_class.Meta.fields
+
+    prefetch_fields = []
+    for field_name in fields_to_include:
+        serializer_field = serializer_class._declared_fields.get(field_name)
+
+        # Determine the name of the model field referenced by the serializer field
+        model_field_name = field_name
+        if serializer_field and serializer_field.source:
+            model_field_name = serializer_field.source
+
+        # If the serializer field does not map to a discrete model field, skip it.
+        try:
+            field = model._meta.get_field(model_field_name)
+            if isinstance(field, (RelatedField, ManyToOneRel, GenericForeignKey)):
+                prefetch_fields.append(field.name)
+        except FieldDoesNotExist:
+            continue
+
+        # If this field is represented by a nested serializer, recurse to resolve prefetches
+        # for the related object.
+        if serializer_field:
+            if issubclass(type(serializer_field), Serializer):
+                for subfield in get_prefetches_for_serializer(type(serializer_field)):
+                    prefetch_fields.append(f'{field_name}__{subfield}')
+
+    return prefetch_fields
+
+
 def rest_api_server_error(request, *args, **kwargs):
     """
     Handle exceptions and return a useful error message for REST API requests.