fix error with PrimaryKeyRelatedField on non-ModelSerializer #353

drf_spectacular/openapi.py

@@ -664,9 +664,17 @@ def _map_serializer_field(self, field, direction, bypass_extensions=False):
                 if isinstance(field.parent, serializers.ManyRelatedField):
                     model = field.parent.parent.Meta.model
                     source = field.parent.source.split('.')
-                else:
+                elif hasattr(field.parent, 'Meta'):
                     model = field.parent.Meta.model
                     source = field.source.split('.')
+                else:
+                    warn(
+                        f'Could not derive type for under-specified PrimaryKeyRelatedField '
+                        f'"{field.field_name}". The serializer has no associated model (Meta class) '
+                        f'and this particular field has no type without a model association. Consider '
+                        f'changing the field or adding a Meta class. defaulting to string.'
+                    )
+                    return append_meta(build_basic_type(OpenApiTypes.STR), meta)
 
                 # estimates the relating model field and jumps to it's target model PK field.
                 # also differentiate as source can be direct (pk) or relation field (model).

tests/test_warnings.py

@@ -500,3 +500,17 @@ def view_func(request, format=None):
     generate_schema('/x/', view_function=view_func)
     stderr = capsys.readouterr().err
     assert 'parameter "test"' in stderr
+
+
+def test_primary_key_related_field_without_serializer_meta(capsys):
+    class XSerializer(serializers.Serializer):
+        field = serializers.PrimaryKeyRelatedField(read_only=True)
+
+    @extend_schema(responses=XSerializer, request=XSerializer)
+    @api_view(['GET'])
+    def view_func(request, format=None):
+        pass  # pragma: no cover
+
+    generate_schema('/x/', view_function=view_func)
+    stderr = capsys.readouterr().err
+    assert 'Could not derive type for under-specified PrimaryKeyRelatedField "field"' in stderr