Merge dd44cee158 into 5420847d9f

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

@@ -222,11 +222,22 @@ 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 a parameter that 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 can not 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 tries to send `q=None`, `q=null` or `q=`, these values will be treated by FastAPI as strings `"None"`, `"null"` and `""` (empty string) respectively.
+
+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] *}
 
 ## Query parameter list / multiple values { #query-parameter-list-multiple-values }
 

docs_src/query_params_str_validations/tutorial006c_an_py310.py

@@ -1,12 +1,21 @@
 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)]):
+async def read_items(
+    q: Annotated[str | None, Query(min_length=3), BeforeValidator(nullable_str)],
+):
     results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
     if q:
         results.update({"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

@@ -4,14 +4,11 @@ import pytest
 from fastapi.testclient import TestClient
 from inline_snapshot import snapshot
 
-from ...utils import needs_py310
-
 
 @pytest.fixture(
     name="client",
     params=[
-        pytest.param("tutorial006c_py310", marks=needs_py310),
-        pytest.param("tutorial006c_an_py310", marks=needs_py310),
+        "tutorial006c_an_py310",
     ],
 )
 def get_client(request: pytest.FixtureRequest):
@@ -22,24 +19,28 @@ def get_client(request: pytest.FixtureRequest):
     return client
 
 
-@pytest.mark.xfail(
-    reason="Code example is not valid. See https://github.com/fastapi/fastapi/issues/12419"
-)
 def test_query_params_str_validations_no_query(client: TestClient):
     response = client.get("/items/")
-    assert response.status_code == 200
-    assert response.json() == {  # pragma: no cover
-        "items": [{"item_id": "Foo"}, {"item_id": "Bar"}],
+    assert response.status_code == 422
+    assert response.json() == {
+        "detail": [
+            {
+                "type": "missing",
+                "loc": ["query", "q"],
+                "msg": "Field required",
+                "input": None,
+            }
+        ]
     }
 
 
-@pytest.mark.xfail(
-    reason="Code example is not valid. See https://github.com/fastapi/fastapi/issues/12419"
-)
-def test_query_params_str_validations_empty_str(client: TestClient):
-    response = client.get("/items/?q=")
+@pytest.mark.parametrize("q_value", ["None", "null", ""])
+def test_query_params_str_validations_send_explicit_none(
+    client: TestClient, q_value: str
+):
+    response = client.get("/items/", params={"q": q_value})
     assert response.status_code == 200
-    assert response.json() == {  # pragma: no cover
+    assert response.json() == {
         "items": [{"item_id": "Foo"}, {"item_id": "Bar"}],
     }