add example/test for DynamicFieldsModelSerializer #375 #912

Also add ``ref_name`` argument to mitigate the naming collision of
parametrized serializers.

https://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields

tests/test_extensions.py

@@ -1,6 +1,7 @@
 from typing import TYPE_CHECKING
 from unittest import mock
 
+from django.contrib.auth.models import User
 from rest_framework import fields, mixins, pagination, permissions, serializers, viewsets
 from rest_framework.authentication import BaseAuthentication
 from rest_framework.decorators import api_view
@@ -15,7 +16,7 @@
     ResolvedComponent, build_array_type, build_basic_type, build_object_type, force_instance,
 )
 from drf_spectacular.types import OpenApiTypes
-from drf_spectacular.utils import Direction, extend_schema, extend_schema_field
+from drf_spectacular.utils import Direction, extend_schema, extend_schema_field, extend_schema_view
 from tests import generate_schema, get_response_schema
 from tests.models import SimpleModel, SimpleSerializer
 
@@ -284,7 +285,7 @@ def __init__(self, serializer_class, pagination_class, **kwargs):
             super().__init__(**kwargs)
 
     class PaginationWrapperExtension(OpenApiSerializerExtension):
-        target_class = PaginationWrapper
+        target_class = PaginationWrapper  # this can also be an import string
 
         def get_name(self, auto_schema, direction):
             return auto_schema.get_paginated_name(
@@ -326,3 +327,66 @@ class XViewset(viewsets.ModelViewSet):
     assert schema['components']['schemas']['PaginatedSimpleList']['properties']['results'] == {
         '$ref': '#/components/schemas/Simple'
     }
+
+
+def test_serializer_with_dynamic_fields(no_warnings):
+    class DynamicFieldsModelSerializer(serializers.ModelSerializer):
+        """
+        A ModelSerializer that takes an additional `fields` argument that
+        controls which fields should be displayed.
+
+        Taken from (only added ref_name)
+        https://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields
+        """
+        def __init__(self, *args, **kwargs):
+            # Don't pass the 'fields' arg up to the superclass
+            fields = kwargs.pop('fields', None)
+            self.ref_name = kwargs.pop('ref_name', None)  # only change to original version!
+
+            # Instantiate the superclass normally
+            super().__init__(*args, **kwargs)
+
+            if fields is not None:
+                # Drop any fields that are not specified in the `fields` argument.
+                allowed = set(fields)
+                existing = set(self.fields)
+                for field_name in existing - allowed:
+                    self.fields.pop(field_name)
+
+    class UserSerializer(DynamicFieldsModelSerializer):
+        class Meta:
+            model = User
+            fields = ['id', 'username', 'email']
+
+    class DynamicFieldsModelSerializerExtension(OpenApiSerializerExtension):
+        target_class = DynamicFieldsModelSerializer  # this can also be an import string
+        match_subclasses = True
+
+        def map_serializer(self, auto_schema: 'AutoSchema', direction: Direction):
+            return auto_schema._map_serializer(self.target, direction, bypass_extensions=True)
+
+        def get_name(self, auto_schema, direction):
+            return self.target.ref_name
+
+    @extend_schema_view(
+        list=extend_schema(responses=UserSerializer(fields=['id'], ref_name='CompactUser'))
+    )
+    class XViewset(viewsets.ModelViewSet):
+        serializer_class = UserSerializer
+        queryset = User.objects.none()
+
+    schema = generate_schema('x', XViewset)
+
+    assert schema['components']['schemas']['User']['properties'] == {
+        'id': {'type': 'integer', 'readOnly': True},
+        'username': {
+            'type': 'string',
+            'description': 'Required. 150 characters or fewer. Letters, digits and @/./+/-/_ only.',
+            'pattern': '^[\\w.@+-]+$',
+            'maxLength': 150
+        },
+        'email': {'type': 'string', 'format': 'email', 'title': 'Email address', 'maxLength': 254}
+    }
+    assert schema['components']['schemas']['CompactUser']['properties'] == {
+        'id': {'type': 'integer', 'readOnly': True}
+    }