Merge 03ca4c106d into 01bb87275b

docs/em/docs/tutorial/query-params-str-validations.md

@@ -154,7 +154,7 @@ q: Union[str, None] = Query(default=None, min_length=3)
 
 👈, 👆 💪 📣 👈 `None` ☑ 🆎 ✋️ ⚙️ `default=...`:
 
-{* ../../docs_src/query_params_str_validations/tutorial006c.py hl[9] *}
+{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9] *}
 
 /// tip
 

docs/en/docs/tutorial/query-params-str-validations.md

@@ -260,11 +260,29 @@ So, when you need to declare a value as required while using `Query`, you can si
 
 ### Required, can be `None` { #required-can-be-none }
 
-You can declare that a parameter can accept `None`, but that it's still required. This would force clients to send a value, even if the value is `None`.
+You might want to declare that a parameter can accept `None`, but is still required.
 
-To do that, you can declare that `None` is a valid type but simply do not declare a default value:
+However, because of how **HTTP query parameters** work, clients cannot actually send a real `None` (or `null`) value — query parameters are always sent as **strings**.
+That means you cannot truly have a *required* parameter that also allows a real `None` value.
 
-{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9] *}
+For example, you might try:
+
+```Python
+q: Annotated[str | None, Query(min_length=3)] = ...
+```
+
+But this will still expect a **string** value, and if the client omits `q` or tries to send `q=None`, FastAPI will raise a **request validation error**.
+In other words, `None` is not an acceptable runtime value for query parameters — only strings are.
+
+If you want to accept special values (like `"None"` or an empty string) and interpret them as `None` in your application, you can handle them manually in your function:
+
+{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9:12,17] *}
+
+/// note
+
+This example uses `BeforeValidator`, which is only available in **Pydantic v2**.
+
+///
 
 ## Query parameter list / multiple values { #query-parameter-list-multiple-values }
 

docs/zh/docs/tutorial/query-params-str-validations.md

@@ -114,7 +114,7 @@ q: Union[str, None] = Query(default=None, min_length=3)
 
 为此，你可以声明`None`是一个有效的类型，并仍然使用`default=...`：
 
-{* ../../docs_src/query_params_str_validations/tutorial006c.py hl[9] *}
+{* ../../docs_src/query_params_str_validations/tutorial006c_an_py310.py hl[9] *}
 
 /// tip
 

docs_src/query_params_str_validations/tutorial006c.py

@@ -1,13 +0,0 @@
-from typing import Union
-
-from fastapi import FastAPI, Query
-
-app = FastAPI()
-
-
-@app.get("/items/")
-async def read_items(q: Union[str, None] = Query(min_length=3)):
-    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
-    if q:
-        results.update({"q": q})
-    return results

docs_src/query_params_str_validations/tutorial006c_an.py

@@ -1,14 +1,20 @@
-from typing import Union
+from typing import Optional, Union
 
 from fastapi import FastAPI, Query
+from pydantic import BeforeValidator
 from typing_extensions import Annotated
 
 app = FastAPI()
 
 
+def nullable_str(val: str) -> Union[str, None]:
+    if val in ("None", "", "null"):
+        return None
+    return val
+
+
 @app.get("/items/")
-async def read_items(q: Annotated[Union[str, None], Query(min_length=3)]):
-    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
-    if q:
-        results.update({"q": q})
-    return results
+async def read_items(
+    q: Annotated[Optional[str], Query(min_length=3), BeforeValidator(nullable_str)],
+):
+    return {"q": q}

docs_src/query_params_str_validations/tutorial006c_an_py310.py

@@ -1,13 +1,19 @@
 from typing import Annotated
 
 from fastapi import FastAPI, Query
+from pydantic import BeforeValidator
 
 app = FastAPI()
 
 
+def nullable_str(val: str) -> str | None:
+    if val in ("None", "", "null"):
+        return None
+    return val
+
+
 @app.get("/items/")
-async def read_items(q: Annotated[str | None, Query(min_length=3)]):
-    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
-    if q:
-        results.update({"q": q})
-    return results
+async def read_items(
+    q: Annotated[str | None, Query(min_length=3), BeforeValidator(nullable_str)],
+):
+    return {"q": q}

docs_src/query_params_str_validations/tutorial006c_an_py39.py

@@ -1,13 +1,19 @@
-from typing import Annotated, Union
+from typing import Annotated, Optional, Union
 
 from fastapi import FastAPI, Query
+from pydantic import BeforeValidator
 
 app = FastAPI()
 
 
+def nullable_str(val: str) -> Union[str, None]:
+    if val in ("None", "", "null"):
+        return None
+    return val
+
+
 @app.get("/items/")
-async def read_items(q: Annotated[Union[str, None], Query(min_length=3)]):
-    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
-    if q:
-        results.update({"q": q})
-    return results
+async def read_items(
+    q: Annotated[Optional[str], Query(min_length=3), BeforeValidator(nullable_str)],
+):
+    return {"q": q}

docs_src/query_params_str_validations/tutorial006c_py310.py

@@ -1,11 +0,0 @@
-from fastapi import FastAPI, Query
-
-app = FastAPI()
-
-
-@app.get("/items/")
-async def read_items(q: str | None = Query(min_length=3)):
-    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
-    if q:
-        results.update({"q": q})
-    return results

tests/test_tutorial/test_query_params_str_validations/test_tutorial006c.py

@@ -0,0 +1,39 @@
+import importlib
+
+import pytest
+from fastapi.testclient import TestClient
+
+from tests.utils import needs_pydanticv2
+
+from ...utils import needs_py39, needs_py310
+
+
+@pytest.fixture(
+    name="client",
+    params=[
+        "tutorial006c_an",
+        pytest.param("tutorial006c_an_py310", marks=needs_py310),
+        pytest.param("tutorial006c_an_py39", marks=needs_py39),
+    ],
+)
+def get_client(request: pytest.FixtureRequest):
+    mod = importlib.import_module(
+        f"docs_src.query_params_str_validations.{request.param}"
+    )
+    yield TestClient(mod.app)
+
+
+@needs_pydanticv2
+@pytest.mark.parametrize(
+    "q_value,expected",
+    [
+        ("None", None),
+        ("", None),
+        ("null", None),
+        ("hello", "hello"),
+    ],
+)
+def test_read_items(q_value, expected, client: TestClient):
+    response = client.get("/items/", params={"q": q_value})
+    assert response.status_code == 200
+    assert response.json() == {"q": expected}