♻️ Use new Pydantic v2 JSON Schema generator (#9813)

Co-authored-by: David Montague <35119617+dmontagu@users.noreply.github.com>

fastapi/_compat.py

@@ -79,6 +79,7 @@ if PYDANTIC_V2:
     class ModelField:
         field_info: FieldInfo
         name: str
+        mode: Literal["validation", "serialization"] = "validation"
 
         @property
         def alias(self) -> str:
@@ -178,9 +179,12 @@ if PYDANTIC_V2:
         field: ModelField,
         schema_generator: GenerateJsonSchema,
         model_name_map: ModelNameMap,
+        field_mapping: Dict[
+            Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue
+        ],
     ) -> Dict[str, Any]:
         # This expects that GenerateJsonSchema was already used to generate the definitions
-        json_schema = schema_generator.generate_inner(field._type_adapter.core_schema)
+        json_schema = field_mapping[(field, field.mode)]
         if "$ref" not in json_schema:
             # TODO remove when deprecating Pydantic v1
             # Ref: https://github.com/pydantic/pydantic/blob/d61792cc42c80b13b23e3ffa74bc37ec7c77f7d1/pydantic/schema.py#L207
@@ -197,12 +201,12 @@ if PYDANTIC_V2:
         fields: List[ModelField],
         schema_generator: GenerateJsonSchema,
         model_name_map: ModelNameMap,
-    ) -> Dict[str, Dict[str, Any]]:
+    ) -> Tuple[Dict[str, Any], Dict[str, Dict[str, Any]]]:
         inputs = [
-            (field, "validation", field._type_adapter.core_schema) for field in fields
+            (field, field.mode, field._type_adapter.core_schema) for field in fields
         ]
-        _, definitions = schema_generator.generate_definitions(inputs=inputs)  # type: ignore[arg-type]
+        field_mapping, definitions = schema_generator.generate_definitions(inputs=inputs)  # type: ignore[arg-type]
-        return definitions  # type: ignore[return-value]
+        return field_mapping, definitions  # type: ignore[return-value]
 
     def is_scalar_field(field: ModelField) -> bool:
         from fastapi import params
@@ -419,6 +423,9 @@ else:
         field: ModelField,
         schema_generator: GenerateJsonSchema,
         model_name_map: ModelNameMap,
+        field_mapping: Dict[
+            Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue
+        ],
     ) -> Dict[str, Any]:
         # This expects that GenerateJsonSchema was already used to generate the definitions
         return field_schema(  # type: ignore[no-any-return]
@@ -434,9 +441,11 @@ else:
         fields: List[ModelField],
         schema_generator: GenerateJsonSchema,
         model_name_map: ModelNameMap,
-    ) -> Dict[str, Dict[str, Any]]:
+    ) -> Tuple[Dict[str, Any], Dict[str, Dict[str, Any]]]:
         models = get_flat_models_from_fields(fields, known_models=set())
-        return get_model_definitions(flat_models=models, model_name_map=model_name_map)
+        return {}, get_model_definitions(
+            flat_models=models, model_name_map=model_name_map
+        )
 
     def is_scalar_field(field: ModelField) -> bool:
         return is_pv1_scalar_field(field)

fastapi/openapi/utils.py

@@ -6,6 +6,7 @@ from typing import Any, Dict, List, Optional, Sequence, Set, Tuple, Type, Union,
 from fastapi import routing
 from fastapi._compat import (
     GenerateJsonSchema,
+    JsonSchemaValue,
     ModelField,
     Undefined,
     get_compat_model_name_map,
@@ -30,6 +31,7 @@ from fastapi.utils import (
 from starlette.responses import JSONResponse
 from starlette.routing import BaseRoute
 from starlette.status import HTTP_422_UNPROCESSABLE_ENTITY
+from typing_extensions import Literal
 
 validation_error_definition = {
     "title": "ValidationError",
@@ -90,6 +92,9 @@ def get_openapi_operation_parameters(
     all_route_params: Sequence[ModelField],
     schema_generator: GenerateJsonSchema,
     model_name_map: ModelNameMap,
+    field_mapping: Dict[
+        Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue
+    ],
 ) -> List[Dict[str, Any]]:
     parameters = []
     for param in all_route_params:
@@ -101,6 +106,7 @@ def get_openapi_operation_parameters(
             field=param,
             schema_generator=schema_generator,
             model_name_map=model_name_map,
+            field_mapping=field_mapping,
         )
         parameter = {
             "name": param.alias,
@@ -123,6 +129,9 @@ def get_openapi_operation_request_body(
     body_field: Optional[ModelField],
     schema_generator: GenerateJsonSchema,
     model_name_map: ModelNameMap,
+    field_mapping: Dict[
+        Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue
+    ],
 ) -> Optional[Dict[str, Any]]:
     if not body_field:
         return None
@@ -131,6 +140,7 @@ def get_openapi_operation_request_body(
         field=body_field,
         schema_generator=schema_generator,
         model_name_map=model_name_map,
+        field_mapping=field_mapping,
     )
     field_info = cast(Body, body_field.field_info)
     request_media_type = field_info.media_type
@@ -198,6 +208,9 @@ def get_openapi_path(
     operation_ids: Set[str],
     schema_generator: GenerateJsonSchema,
     model_name_map: ModelNameMap,
+    field_mapping: Dict[
+        Tuple[ModelField, Literal["validation", "serialization"]], JsonSchemaValue
+    ],
 ) -> Tuple[Dict[str, Any], Dict[str, Any], Dict[str, Any]]:
     path = {}
     security_schemes: Dict[str, Any] = {}
@@ -228,6 +241,7 @@ def get_openapi_path(
                 all_route_params=all_route_params,
                 schema_generator=schema_generator,
                 model_name_map=model_name_map,
+                field_mapping=field_mapping,
             )
             parameters.extend(operation_parameters)
             if parameters:
@@ -248,6 +262,7 @@ def get_openapi_path(
                     body_field=route.body_field,
                     schema_generator=schema_generator,
                     model_name_map=model_name_map,
+                    field_mapping=field_mapping,
                 )
                 if request_body_oai:
                     operation["requestBody"] = request_body_oai
@@ -264,6 +279,7 @@ def get_openapi_path(
                             operation_ids=operation_ids,
                             schema_generator=schema_generator,
                             model_name_map=model_name_map,
+                            field_mapping=field_mapping,
                         )
                         callbacks[callback.name] = {callback.path: cb_path}
                 operation["callbacks"] = callbacks
@@ -293,6 +309,7 @@ def get_openapi_path(
                             field=route.response_field,
                             schema_generator=schema_generator,
                             model_name_map=model_name_map,
+                            field_mapping=field_mapping,
                         )
                     else:
                         response_schema = {}
@@ -325,6 +342,7 @@ def get_openapi_path(
                             field=field,
                             schema_generator=schema_generator,
                             model_name_map=model_name_map,
+                            field_mapping=field_mapping,
                         )
                         media_type = route_response_media_type or "application/json"
                         additional_schema = (
@@ -437,7 +455,7 @@ def get_openapi(
     all_fields = get_fields_from_routes(list(routes or []) + list(webhooks or []))
     model_name_map = get_compat_model_name_map(all_fields)
     schema_generator = GenerateJsonSchema(ref_template=REF_TEMPLATE)
-    definitions = get_definitions(
+    field_mapping, definitions = get_definitions(
         fields=all_fields,
         schema_generator=schema_generator,
         model_name_map=model_name_map,
@@ -449,6 +467,7 @@ def get_openapi(
                 operation_ids=operation_ids,
                 schema_generator=schema_generator,
                 model_name_map=model_name_map,
+                field_mapping=field_mapping,
             )
             if result:
                 path, security_schemes, path_definitions = result
@@ -467,6 +486,7 @@ def get_openapi(
                 operation_ids=operation_ids,
                 schema_generator=schema_generator,
                 model_name_map=model_name_map,
+                field_mapping=field_mapping,
             )
             if result:
                 path, security_schemes, path_definitions = result

fastapi/routing.py

@@ -446,7 +446,11 @@ class APIRoute(routing.Route):
             ), f"Status code {status_code} must not have a response body"
             response_name = "Response_" + self.unique_id
             self.response_field = create_response_field(
-                name=response_name, type_=self.response_model
+                name=response_name,
+                type_=self.response_model,
+                # TODO: This should actually set mode='serialization', just, that changes the schemas
+                # mode="serialization",
+                mode="validation",
             )
             # Create a clone of the field, so that a Pydantic submodel is not returned
             # as is just because it's an instance of a subclass of a more limited class

fastapi/utils.py

@@ -28,6 +28,7 @@ from fastapi._compat import (
 from fastapi.datastructures import DefaultPlaceholder, DefaultType
 from pydantic import BaseModel, create_model
 from pydantic.fields import FieldInfo
+from typing_extensions import Literal
 
 if TYPE_CHECKING:  # pragma: nocover
     from .routing import APIRoute
@@ -68,6 +69,7 @@ def create_response_field(
     model_config: Type[BaseConfig] = BaseConfig,
     field_info: Optional[FieldInfo] = None,
     alias: Optional[str] = None,
+    mode: Literal["validation", "serialization"] = "validation",
 ) -> ModelField:
     """
     Create a new response field. Raises if type_ is invalid.
@@ -80,7 +82,9 @@ def create_response_field(
     else:
         field_info = field_info or FieldInfo()
     kwargs = {"name": name, "field_info": field_info}
-    if not PYDANTIC_V2:
+    if PYDANTIC_V2:
+        kwargs.update({"mode": mode})
+    else:
         kwargs.update(
             {
                 "type_": type_,