rm being able to determine the input format of a model

docs/en/docs/tutorial/request-form-models.md

@@ -107,33 +107,34 @@ and [the field will be omitted altogether if unchecked](https://developer.mozill
 When dealing with form models with defaults,
 we need to take special care to handle cases where the field being *unset* has a specific meaning.
 
+We also don't want to just treat any time the value is unset as ``False`` -
+that would defeat the purpose of the default!
+We want to specifically correct the behavior when it is used in the context of a *form.*
+
 In some cases, we can resolve the problem by changing or removing the default,
 but we don't always have that option -
 particularly when the model is used in other places than the form
 (model reuse is one of the benefits of building FastAPI on top of pydantic, after all!).
 
-To do this, you can use a [`model_validator`](https://docs.pydantic.dev/latest/concepts/validators/#model-validators)
+The recommended approach, however, is to duplicate your model:
-in the `before` mode - before the defaults from the model are applied,
-to differentiate between an explicit `False` value and an unset value.
-
-We also don't want to just treat any time the value is unset as ``False`` -
-that would defeat the purpose of the default!
-We want to specifically correct the behavior when it is used in the context of a *form.*
-
-So we can additionally use the `'fastapi_field'` passed to the
-[validation context](https://docs.pydantic.dev/latest/concepts/validators/#validation-context)
-to determine whether our model is being validated from form input.
 
 /// note
 
-Validation context is a pydantic v2 only feature!
+Take care to ensure that your duplicate models don't diverge,
+particularly if you are using sqlmodel,
+where you will end up with `MyModel`, `MyModelCreate`, and `MyModelCreateForm`.
+
+Also remember to make sure that anywhere else you use this model adds the appropriate
+switching logic and static type annotations to accommodate receiving both the original class
+and the model we make as a workaround for form handling.
 
 ///
 
 {* ../../docs_src/request_form_models/tutorial004_an_py39.py hl[7,13:25] *}
 
-And with that, our form model should behave as expected when it is used with a form,
+And with that, one of our models should behave as expected when used with a form,
-JSON input, or elsewhere in the program!
+and you can switch between it and other permutations of the model for JSON input
+or any other format you may need to handle!
 
 ## Summary
 

docs_src/request_form_models/tutorial004.py

@@ -1,24 +1,20 @@
+from typing import cast
+
 from fastapi import FastAPI, Form, Request
 from fastapi.responses import HTMLResponse
 from fastapi.templating import Jinja2Templates
 from jinja2 import DictLoader, Environment
-from pydantic import BaseModel, ValidationInfo, model_validator
+from pydantic import BaseModel, model_validator
 
 
 class MyModel(BaseModel):
     checkbox: bool = True
 
+
+class MyModelForm(MyModel):
     @model_validator(mode="before")
-    def handle_defaults(cls, value: dict, info: ValidationInfo) -> dict:
+    def handle_defaults(cls, value: dict) -> dict:
-        # if this model is being used outside of fastapi, return normally
+        if "checkbox" not in value:
-        if info.context is None or "fastapi_field" not in info.context:
-            return value
-
-        # check if we are being validated from form input,
-        # and if so, treat the unset checkbox as False
-        field_info = info.context["fastapi_field"].field_info
-        is_form = type(field_info).__name__ == "Form"
-        if is_form and "checkbox" not in value:
             value["checkbox"] = False
         return value
 
@@ -56,5 +52,6 @@ async def show_form(request: Request):
 
 
 @app.post("/form")
-async def submit_form(data: MyModel = Form()) -> MyModel:
+async def submit_form(data: MyModelForm = Form()) -> MyModel:
+    data = cast(MyModel, data)
     return data

docs_src/request_form_models/tutorial004_an_py39.py

@@ -1,4 +1,4 @@
-from typing import Annotated
+from typing import Annotated, cast
 
 from fastapi import FastAPI, Form, Request
 from fastapi.responses import HTMLResponse
@@ -10,17 +10,11 @@ from pydantic import BaseModel, ValidationInfo, model_validator
 class MyModel(BaseModel):
     checkbox: bool = True
 
+
+class MyModelForm(MyModel):
     @model_validator(mode="before")
     def handle_defaults(cls, value: dict, info: ValidationInfo) -> dict:
-        # if this model is being used outside of fastapi, return normally
+        if "checkbox" not in value:
-        if info.context is None or "fastapi_field" not in info.context:
-            return value
-
-        # check if we are being validated from form input,
-        # and if so, treat the unset checkbox as False
-        field_info = info.context["fastapi_field"].field_info
-        is_form = type(field_info).__name__ == "Form"
-        if is_form and "checkbox" not in value:
             value["checkbox"] = False
         return value
 
@@ -58,5 +52,6 @@ async def show_form(request: Request):
 
 
 @app.post("/form")
-async def submit_form(data: Annotated[MyModel, Form()]) -> MyModel:
+async def submit_form(data: Annotated[MyModelForm, Form()]) -> MyModel:
+    data = cast(MyModel, data)
     return data

docs_src/request_form_models/tutorial004_pv1.py

@@ -1,3 +1,5 @@
+from typing import cast
+
 from fastapi import FastAPI, Form, Request
 from fastapi.responses import HTMLResponse
 from fastapi.templating import Jinja2Templates
@@ -8,10 +10,10 @@ from pydantic import BaseModel, root_validator
 class MyModel(BaseModel):
     checkbox: bool = True
 
+
+class MyModelForm(BaseModel):
     @root_validator(pre=True)
     def handle_defaults(cls, value: dict) -> dict:
-        # We can't tell if we're being validated by fastAPI,
-        # so we have to just YOLO this.
         if "checkbox" not in value:
             value["checkbox"] = False
         return value
@@ -50,5 +52,6 @@ async def show_form(request: Request):
 
 
 @app.post("/form")
-async def submit_form(data: MyModel = Form()) -> MyModel:
+async def submit_form(data: MyModelForm = Form()) -> MyModel:
+    data = cast(MyModel, data)
     return data

docs_src/request_form_models/tutorial004_pv1_an_py39.py

@@ -1,4 +1,4 @@
-from typing import Annotated
+from typing import Annotated, cast
 
 from fastapi import FastAPI, Form, Request
 from fastapi.responses import HTMLResponse
@@ -10,10 +10,10 @@ from pydantic import BaseModel, root_validator
 class MyModel(BaseModel):
     checkbox: bool = True
 
+
+class MyModelForm(MyModel):
     @root_validator(pre=True)
     def handle_defaults(cls, value: dict) -> dict:
-        # We can't tell if we're being validated by fastAPI,
-        # so we have to just YOLO this.
         if "checkbox" not in value:
             value["checkbox"] = False
         return value
@@ -52,5 +52,6 @@ async def show_form(request: Request):
 
 
 @app.post("/form")
-async def submit_form(data: Annotated[MyModel, Form()]) -> MyModel:
+async def submit_form(data: Annotated[MyModelForm, Form()]) -> MyModel:
+    data = cast(MyModel, data)
     return data

fastapi/_compat.py

@@ -126,9 +126,7 @@ if PYDANTIC_V2:
         ) -> Tuple[Any, Union[List[Dict[str, Any]], None]]:
             try:
                 return (
-                    self._type_adapter.validate_python(
+                    self._type_adapter.validate_python(value, from_attributes=True),
-                        value, from_attributes=True, context={"fastapi_field": self}
-                    ),
                     None,
                 )
             except ValidationError as exc: