Merge 01152f60dd into 272204c0c7

fastapi/applications.py

@@ -979,6 +979,7 @@ class FastAPI(Starlette):
             include_in_schema=include_in_schema,
             responses=responses,
             generate_unique_id_function=generate_unique_id_function,
+            defer_init=False,
         )
         self.exception_handlers: Dict[
             Any, Callable[[Request, Any], Union[Response, Awaitable[Response]]]

fastapi/routing.py

@@ -5,6 +5,7 @@ import inspect
 import json
 from contextlib import AsyncExitStack, asynccontextmanager
 from enum import Enum, IntEnum
+from functools import cached_property
 from typing import (
     Any,
     AsyncIterator,
@@ -591,6 +592,7 @@ class APIRoute(routing.Route):
         generate_unique_id_function: Union[
             Callable[["APIRoute"], str], DefaultPlaceholder
         ] = Default(generate_unique_id),
+        defer_init: bool = True,
     ) -> None:
         self.path = path
         self.endpoint = endpoint
@@ -639,31 +641,42 @@ class APIRoute(routing.Route):
             assert is_body_allowed_for_status_code(status_code), (
                 f"Status code {status_code} must not have a response body"
             )
-            response_name = "Response_" + self.unique_id
-            self.response_field = create_model_field(
-                name=response_name,
-                type_=self.response_model,
-                mode="serialization",
-            )
-            # 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
-            # e.g. UserInDB (containing hashed_password) could be a subclass of User
-            # that doesn't have the hashed_password. But because it's a subclass, it
-            # would pass the validation and be returned as is.
-            # By being a new field, no inheritance will be passed as is. A new model
-            # will always be created.
-            # TODO: remove when deprecating Pydantic v1
-            self.secure_cloned_response_field: Optional[ModelField] = (
-                create_cloned_field(self.response_field)
-            )
-        else:
-            self.response_field = None  # type: ignore
-            self.secure_cloned_response_field = None
         self.dependencies = list(dependencies or [])
         self.description = description or inspect.cleandoc(self.endpoint.__doc__ or "")
         # if a "form feed" character (page break) is found in the description text,
         # truncate description text to the content preceding the first "form feed"
         self.description = self.description.split("\f")[0].strip()
+
+        assert callable(endpoint), "An endpoint must be a callable"
+
+        if not defer_init:
+            self.init_attributes()
+
+    @cached_property
+    def response_field(self) -> Optional[ModelField]:
+        if not self.response_model:
+            return None
+        response_name = "Response_" + self.unique_id
+        return create_model_field(
+            name=response_name,
+            type_=self.response_model,
+            mode="serialization",
+        )
+
+    @cached_property
+    def secure_cloned_response_field(self) -> Optional[ModelField]:
+        # 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
+        # e.g. UserInDB (containing hashed_password) could be a subclass of User
+        # that doesn't have the hashed_password. But because it's a subclass, it
+        # would pass the validation and be returned as is.
+        # By being a new field, no inheritance will be passed as is. A new model
+        # will always be created.
+        # TODO: remove when deprecating Pydantic v1
+        return create_cloned_field(self.response_field) if self.response_field else None
+
+    @cached_property
+    def response_fields(self) -> Dict[Union[int, str], ModelField]:
         response_fields = {}
         for additional_status_code, response in self.responses.items():
             assert isinstance(response, dict), "An additional response must be a dict"
@@ -677,30 +690,49 @@ class APIRoute(routing.Route):
                     name=response_name, type_=model, mode="serialization"
                 )
                 response_fields[additional_status_code] = response_field
-        if response_fields:
-            self.response_fields: Dict[Union[int, str], ModelField] = response_fields
-        else:
-            self.response_fields = {}
+        return response_fields
 
-        assert callable(endpoint), "An endpoint must be a callable"
-        self.dependant = get_dependant(
+    @cached_property
+    def dependant(self) -> Dependant:
+        dependant = get_dependant(
             path=self.path_format, call=self.endpoint, scope="function"
         )
         for depends in self.dependencies[::-1]:
-            self.dependant.dependencies.insert(
+            dependant.dependencies.insert(
                 0,
                 get_parameterless_sub_dependant(depends=depends, path=self.path_format),
             )
-        self._flat_dependant = get_flat_dependant(self.dependant)
-        self._embed_body_fields = _should_embed_body_fields(
-            self._flat_dependant.body_params
-        )
-        self.body_field = get_body_field(
+        return dependant
+
+    @cached_property
+    def _flat_dependant(self) -> Dependant:
+        return get_flat_dependant(self.dependant)
+
+    @cached_property
+    def _embed_body_fields(self) -> bool:
+        return _should_embed_body_fields(self._flat_dependant.body_params)
+
+    @cached_property
+    def body_field(self) -> Optional[ModelField]:
+        return get_body_field(
             flat_dependant=self._flat_dependant,
             name=self.unique_id,
             embed_body_fields=self._embed_body_fields,
         )
-        self.app = request_response(self.get_route_handler())
+
+    @cached_property
+    def app(self) -> ASGIApp:  # type: ignore
+        return request_response(self.get_route_handler())
+
+    def init_attributes(self) -> None:
+        _ = self.app
+        _ = self.dependant
+        _ = self.response_field
+        _ = self.response_fields
+        _ = self.secure_cloned_response_field
+        _ = self.body_field
+        _ = self._flat_dependant
+        _ = self._embed_body_fields
 
     def get_route_handler(self) -> Callable[[Request], Coroutine[Any, Any, Response]]:
         return get_request_handler(
@@ -967,6 +999,16 @@ class APIRouter(routing.Router):
                 """
             ),
         ] = Default(generate_unique_id),
+        defer_init: Annotated[
+            bool,
+            Doc(
+                """
+                By default, every route will defer its initialization until the first call.
+                This flag can be used to deactivate this behavior for the routes defined in this router,
+                causing the routes to initialize immediately when they are defined.
+                """
+            ),
+        ] = True,
     ) -> None:
         super().__init__(
             routes=routes,
@@ -992,6 +1034,9 @@ class APIRouter(routing.Router):
         self.route_class = route_class
         self.default_response_class = default_response_class
         self.generate_unique_id_function = generate_unique_id_function
+        self.defer_init = defer_init
+        if not self.defer_init:
+            self.init_routes()
 
     def route(
         self,
@@ -1091,6 +1136,7 @@ class APIRouter(routing.Router):
             callbacks=current_callbacks,
             openapi_extra=openapi_extra,
             generate_unique_id_function=current_generate_unique_id,
+            defer_init=self.defer_init,
         )
         self.routes.append(route)
 
@@ -1253,6 +1299,11 @@ class APIRouter(routing.Router):
 
         return decorator
 
+    def init_routes(self) -> None:
+        for route in self.routes:
+            if isinstance(route, APIRoute):
+                route.init_attributes()
+
     def include_router(
         self,
         router: Annotated["APIRouter", Doc("The `APIRouter` to include.")],

tests/test_route_deferred_init.py

@@ -0,0 +1,117 @@
+from itertools import chain
+from typing import List, Optional
+
+from fastapi import APIRouter, Depends, FastAPI
+from fastapi.routing import APIRoute
+from fastapi.testclient import TestClient
+from pydantic import BaseModel
+from starlette.routing import BaseRoute
+
+deferred_keys = [
+    "app",
+    "response_fields",
+    "body_field",
+    "response_field",
+    "secure_cloned_response_field",
+    "dependant",
+    "_flat_dependant",
+    "_embed_body_fields",
+]
+
+
+def check_if_initialized(route: APIRoute, should_not: bool = False):
+    for key in deferred_keys:
+        if should_not:
+            assert key not in route.__dict__
+        else:
+            assert key in route.__dict__
+
+
+def create_test_router(
+    routes: Optional[List[BaseRoute]] = None, defer_init: bool = True
+):
+    router = APIRouter(routes=routes or [], defer_init=defer_init)
+
+    class UserIdBody(BaseModel):
+        user_id: int
+
+    @router.get("/user_id", dependencies=[Depends(lambda: True)])
+    async def get_user_id(user_id: int = Depends(lambda: 1)) -> UserIdBody:
+        return {"user_id": user_id}
+
+    return router
+
+
+def test_route_defers():
+    app = FastAPI()
+    router = create_test_router(routes=app.router.routes)
+
+    for route in router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route, should_not=True)
+
+    app.router = router
+    client = TestClient(app)
+    response = client.get("/user_id")
+    assert response.status_code == 200
+    response = client.get("/openapi.json")
+    assert response.status_code == 200
+
+    for route in router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route)
+
+
+def test_route_manual_init():
+    router = create_test_router()
+    for route in router.routes:
+        check_if_initialized(route, should_not=True)
+        route.init_attributes()
+        check_if_initialized(route)
+
+    router = create_test_router()
+    router.init_routes()
+    for route in router.routes:
+        check_if_initialized(route)
+
+
+def test_router_defer_init_flag():
+    route = APIRoute("/test", lambda: {"test": True}, defer_init=False)
+    check_if_initialized(route)
+
+    deferring_router = create_test_router()
+    router = create_test_router(routes=deferring_router.routes, defer_init=False)
+
+    for route in router.routes:
+        check_if_initialized(route)
+
+
+def test_root_router_always_initialized():
+    app = FastAPI()
+
+    @app.get("/test")
+    async def test_get():
+        return {"test": 1}
+
+    router = create_test_router()
+    app.include_router(router)
+    for route in app.router.routes:
+        if not isinstance(route, APIRoute):
+            continue
+        check_if_initialized(route)
+
+    client = TestClient(app)
+    response = client.get("/test")
+    assert response.status_code == 200
+
+
+def test_include_router_no_init():
+    router1 = create_test_router()
+
+    router2 = create_test_router()
+    router2.include_router(router1)
+
+    for route in chain(router1.routes, router2.routes):
+        check_if_initialized(route, should_not=True)