查询参数与字符串验证¶

FastAPI 允许你为参数声明额外的信息和验证。

以下面这个应用为例：

Python 3.10+

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.8+

from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

查询参数 q 的类型是 str | None，这意味着它可以是 str 类型，也可以是 None，实际上默认值就是 None，所以 FastAPI 会知道它不是必需的。

Note

FastAPI 会知道 q 的值不是必需的，因为默认值是 = None。

使用 str | None 可以让你的编辑器提供更好的支持并检测错误。

额外验证¶

我们将强制要求即使 q 是可选的，但只要提供了，其长度不能超过 50 个字符。

导入 `Query` 和 `Annotated`¶

为了实现这一点，首先导入：

fastapi 中的 Query
typing 中的 Annotated

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str | None, Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Info

FastAPI 在 0.95.0 版本中添加了对 Annotated 的支持（并开始推荐使用）。

如果你使用的是旧版本，尝试使用 Annotated 时会出错。

确保在使用 Annotated 之前将 FastAPI 版本升级到至少 0.95.1。

在 `q` 参数的类型中使用 `Annotated`¶

还记得我之前在 Python 类型介绍中提到过 Annotated 可以用来为参数添加元数据吗？

现在是时候在 FastAPI 中使用它了。🚀

我们原本的类型注解是这样的：

Python 3.10+Python 3.8+

q: str | None = None

q: Union[str, None] = None

我们要做的是用 Annotated 包装它，变成：

Python 3.10+Python 3.8+

q: Annotated[str | None] = None

q: Annotated[Union[str, None]] = None

这两个版本的意思相同，q 是一个可以是 str 或 None 的参数，默认情况下是 None。

现在让我们进入有趣的部分。🎉

在 `q` 参数中将 `Query` 添加到 `Annotated`¶

现在我们有了这个 Annotated，可以在其中放入更多信息（在这里是一些额外的验证），将 Query 放入 Annotated 中，并将参数 max_length 设置为 50：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str | None, Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

注意默认值仍然是 None，所以参数仍然是可选的。

但现在，通过在 Annotated 中加入 Query(max_length=50)，我们告诉 FastAPI 我们希望对这个值进行额外的验证，即最大长度为 50 个字符。😎

Tip

这里我们使用 Query() 是因为这是一个查询参数。稍后我们会看到其他类似的如 Path()、Body()、Header() 和 Cookie()，它们也接受与 Query() 相同的参数。

FastAPI 现在会：

验证数据，确保最大长度为 50 个字符
当数据无效时，向客户端显示清晰的错误
在 OpenAPI 模式的路径操作中记录该参数（因此它会显示在自动文档 UI 中）

替代方案（旧）：将 `Query` 作为默认值¶

旧版本的 FastAPI（在 0.95.0 之前）要求你将 Query 作为参数的默认值，而不是放在 Annotated 中，你可能会在代码中看到这种用法，所以我解释一下。

Tip

对于新代码，尽可能使用 Annotated，如上所述。这样做有多种优势（如下所述），且没有缺点。🍰

这是你如何使用 Query() 作为函数参数的默认值，将参数 max_length 设置为 50：

Python 3.10+ - non-Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.10+Python 3.8+Python 3.8+ - non-Annotated

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str | None, Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(max_length=50)] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = Query(default=None, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

在这种情况下（不使用 Annotated），我们必须将函数中的默认值 None 替换为 Query()，现在需要用参数 Query(default=None) 设置默认值，它的作用与定义默认值相同（至少对 FastAPI 来说）。

所以：

q: str | None = Query(default=None)

...使参数可选，默认值为 None，与以下代码相同：

q: str | None = None

但 Query 版本明确声明它是一个查询参数。

然后，我们可以向 Query 传递更多参数。在这里是适用于字符串的 max_length 参数：

q: str | None = Query(default=None, max_length=50)

这将验证数据，在数据无效时显示清晰的错误，并在 OpenAPI 模式的路径操作中记录该参数。

将 `Query` 作为默认值或在 `Annotated` 中¶

记住，在 Annotated 中使用 Query 时，不能使用 Query 的 default 参数。

相反，应使用函数参数的实际默认值。否则会不一致。

例如，以下是不允许的：

q: Annotated[str, Query(default="rick")] = "morty"

...因为不清楚默认值应该是 "rick" 还是 "morty"。

所以，你应该使用（推荐）：

q: Annotated[str, Query()] = "rick"

...或者在旧代码库中你会看到：

q: str = Query(default="rick")

`Annotated` 的优势¶

推荐使用 Annotated 而不是函数参数中的默认值，这样做有多个原因。🤓

函数参数的默认值是实际的默认值，这在 Python 中更直观。😌

你可以在其他地方调用相同的函数而不使用 FastAPI，它会按预期工作。如果有一个必需的参数（没有默认值），你的编辑器会通过错误提示告诉你，Python 也会在运行时不传递必需参数时报错。

当你不使用 Annotated 而使用（旧的）默认值风格时，如果在其他地方调用该函数而不使用 FastAPI，你必须记住传递参数才能使函数正常工作，否则值会与你预期的不同（例如 QueryInfo 或类似的东西而不是 str）。你的编辑器不会报错，Python 也不会在运行该函数时报错，只有在内部操作出错时才会报错。

因为 Annotated 可以有多个元数据注解，你现在甚至可以将相同的函数与其他工具一起使用，比如 Typer。🚀

添加更多验证¶

你还可以添加一个 min_length 参数：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[str | None, Query(min_length=3, max_length=50)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[Union[str, None], Query(min_length=3, max_length=50)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[Union[str, None], Query(min_length=3, max_length=50)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = Query(default=None, min_length=3, max_length=50)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(default=None, min_length=3, max_length=50),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

添加正则表达式¶

你可以定义一个正则表达式 pattern，参数值必须匹配该模式：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        str | None, Query(min_length=3, max_length=50, pattern="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None], Query(min_length=3, max_length=50, pattern="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None], Query(min_length=3, max_length=50, pattern="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: str | None = Query(
        default=None, min_length=3, max_length=50, pattern="^fixedquery$"
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None, min_length=3, max_length=50, pattern="^fixedquery$"
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

这个特定的正则表达式模式检查接收到的参数值：

^：以以下字符开头，前面没有其他字符。
fixedquery：具有确切值 fixedquery。
$：在此结束，fixedquery 后面没有其他字符。

如果你对这些“正则表达式”概念感到困惑，别担心。对许多人来说这是一个难题。你仍然可以在不需要正则表达式的情况下做很多事情。

现在你知道，当你需要它们时，可以在 FastAPI 中使用它们。

Pydantic v1 的 `regex` 而非 `pattern`¶

在 Pydantic 版本 2 和 FastAPI 0.100.0 之前，参数名为 regex 而不是 pattern，但现在已弃用。

你仍可能看到一些代码在使用它：

Pydantic v1

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        str | None, Query(min_length=3, max_length=50, regex="^fixedquery$")
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

但要知道这已被弃用，应更新为使用新参数 pattern。🤓

默认值¶

当然，你可以使用 None 以外的默认值。

假设你想声明 q 查询参数的 min_length 为 3，并设置默认值为 "fixedquery"：

Python 3.9+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str, Query(min_length=3)] = "fixedquery"):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str, Query(min_length=3)] = "fixedquery"):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str = Query(default="fixedquery", min_length=3)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Note

任何类型的默认值，包括 None，都会使参数变为可选（非必需）。

必需参数¶

当我们不需要声明更多验证或元数据时，可以通过不声明默认值来使 q 查询参数成为必需，例如：

q: str

而不是：

q: str | None = None

但我们现在是用 Query 声明它，例如：

Annotated

q: Annotated[str | None, Query(min_length=3)] = None

因此，当需要使用 Query 声明一个必需参数时，可以简单地不声明默认值：

Python 3.9+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str, Query(min_length=3)]):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str, Query(min_length=3)]):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str = Query(min_length=3)):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

必需但可以是 `None`¶

你可以声明一个参数可以接受 None，但它仍然是必需的。这将强制客户端发送一个值，即使该值是 None。

为此，你可以声明 None 是一个有效类型但不声明默认值：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@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

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@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

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@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

Tip

Prefer to use the Annotated version if possible.

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

Tip

Prefer to use the Annotated version if possible.

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

查询参数列表 / 多值¶

当你用 Query 显式定义一个查询参数时，还可以声明它接收一个值列表，或者说接收多个值。

例如，要声明一个可以在 URL 中出现多次的查询参数 q，你可以这样写：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list[str] | None, Query()] = None):
    query_items = {"q": q}
    return query_items

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.9+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[list[str], None], Query()] = None):
    query_items = {"q": q}
    return query_items

from typing import List, Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[List[str], None], Query()] = None):
    query_items = {"q": q}
    return query_items

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: list[str] | None = Query(default=None)):
    query_items = {"q": q}
    return query_items

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[list[str], None] = Query(default=None)):
    query_items = {"q": q}
    return query_items

Tip

Prefer to use the Annotated version if possible.

from typing import List, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[List[str], None] = Query(default=None)):
    query_items = {"q": q}
    return query_items

然后，对于这样的 URL：

http://localhost:8000/items/?q=foo&q=bar

你会在路径操作函数的函数参数 q 中以 Python list 的形式接收到多个 q 查询参数的值（foo 和 bar）。

因此，该 URL 的响应将是：

{
  "q": [
    "foo",
    "bar"
  ]
}

Tip

要声明一个类型为 list 的查询参数，如上例所示，你需要显式使用 Query，否则它会被解释为请求体。

交互式 API 文档将相应更新，以允许多个值：

带默认值的查询参数列表 / 多值¶

你还可以定义一个默认的 list 值，如果没有提供值：

Python 3.9+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list[str], Query()] = ["foo", "bar"]):
    query_items = {"q": q}
    return query_items

🤓 Other versions and variants

Python 3.8+Python 3.9+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import List

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[List[str], Query()] = ["foo", "bar"]):
    query_items = {"q": q}
    return query_items

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: list[str] = Query(default=["foo", "bar"])):
    query_items = {"q": q}
    return query_items

Tip

Prefer to use the Annotated version if possible.

from typing import List

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: List[str] = Query(default=["foo", "bar"])):
    query_items = {"q": q}
    return query_items

如果你访问：

http://localhost:8000/items/

q 的默认值将是：["foo", "bar"]，你的响应将是：

{
  "q": [
    "foo",
    "bar"
  ]
}

仅使用 `list`¶

你也可以直接使用 list 而不是 list[str]：

Python 3.9+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list, Query()] = []):
    query_items = {"q": q}
    return query_items

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[list, Query()] = []):
    query_items = {"q": q}
    return query_items

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: list = Query(default=[])):
    query_items = {"q": q}
    return query_items

Note

请注意，在这种情况下，FastAPI 不会检查列表的内容。

例如，list[int] 会检查（并记录）列表内容是整数。但仅使用 list 则不会。

声明更多元数据¶

你可以添加关于参数的更多信息。

这些信息将包含在生成的 OpenAPI 中，并被文档用户界面和外部工具使用。

Note

请注意，不同的工具对 OpenAPI 的支持程度可能不同。

其中一些可能尚未显示所有声明的额外信息，尽管在大多数情况下，缺失的功能已经在开发计划中。

你可以添加一个 title：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[str | None, Query(title="Query string", min_length=3)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[Union[str, None], Query(title="Query string", min_length=3)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[Union[str, None], Query(title="Query string", min_length=3)] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: str | None = Query(default=None, title="Query string", min_length=3),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(default=None, title="Query string", min_length=3),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

以及一个 description：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        str | None,
        Query(
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: str | None = Query(
        default=None,
        title="Query string",
        description="Query string for the items to search in the database that have a good match",
        min_length=3,
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None,
        title="Query string",
        description="Query string for the items to search in the database that have a good match",
        min_length=3,
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

别名参数¶

假设你希望参数名为 item-query。

例如：

http://127.0.0.1:8000/items/?item-query=foobaritems

但 item-query 不是一个有效的 Python 变量名。

最接近的是 item_query。

但你仍然希望它是 item-query...

这时你可以声明一个 alias，这个别名将用于查找参数值：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[str | None, Query(alias="item-query")] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(alias="item-query")] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(q: Annotated[Union[str, None], Query(alias="item-query")] = None):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: str | None = Query(default=None, alias="item-query")):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(q: Union[str, None] = Query(default=None, alias="item-query")):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

弃用参数¶

假设你现在不再喜欢这个参数。

由于有客户端在使用它，你需要暂时保留它，但你希望文档明确显示它为弃用。

然后将参数 deprecated=True 传递给 Query：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        str | None,
        Query(
            alias="item-query",
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
            max_length=50,
            pattern="^fixedquery$",
            deprecated=True,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            alias="item-query",
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
            max_length=50,
            pattern="^fixedquery$",
            deprecated=True,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Annotated[
        Union[str, None],
        Query(
            alias="item-query",
            title="Query string",
            description="Query string for the items to search in the database that have a good match",
            min_length=3,
            max_length=50,
            pattern="^fixedquery$",
            deprecated=True,
        ),
    ] = None,
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: str | None = Query(
        default=None,
        alias="item-query",
        title="Query string",
        description="Query string for the items to search in the database that have a good match",
        min_length=3,
        max_length=50,
        pattern="^fixedquery$",
        deprecated=True,
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    q: Union[str, None] = Query(
        default=None,
        alias="item-query",
        title="Query string",
        description="Query string for the items to search in the database that have a good match",
        min_length=3,
        max_length=50,
        pattern="^fixedquery$",
        deprecated=True,
    ),
):
    results = {"items": [{"item_id": "Foo"}, {"item_id": "Bar"}]}
    if q:
        results.update({"q": q})
    return results

文档将显示如下：

从 OpenAPI 中排除参数¶

要从生成的 OpenAPI 模式（以及自动文档系统）中排除查询参数，将 Query 的参数 include_in_schema 设置为 False：

Python 3.10+

from typing import Annotated

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    hidden_query: Annotated[str | None, Query(include_in_schema=False)] = None,
):
    if hidden_query:
        return {"hidden_query": hidden_query}
    else:
        return {"hidden_query": "Not found"}

🤓 Other versions and variants

Python 3.9+Python 3.8+Python 3.10+ - non-AnnotatedPython 3.8+ - non-Annotated

from typing import Annotated, Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    hidden_query: Annotated[Union[str, None], Query(include_in_schema=False)] = None,
):
    if hidden_query:
        return {"hidden_query": hidden_query}
    else:
        return {"hidden_query": "Not found"}

from typing import Union

from fastapi import FastAPI, Query
from typing_extensions import Annotated

app = FastAPI()


@app.get("/items/")
async def read_items(
    hidden_query: Annotated[Union[str, None], Query(include_in_schema=False)] = None,
):
    if hidden_query:
        return {"hidden_query": hidden_query}
    else:
        return {"hidden_query": "Not found"}

Tip

Prefer to use the Annotated version if possible.

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    hidden_query: str | None = Query(default=None, include_in_schema=False),
):
    if hidden_query:
        return {"hidden_query": hidden_query}
    else:
        return {"hidden_query": "Not found"}

Tip

Prefer to use the Annotated version if possible.

from typing import Union

from fastapi import FastAPI, Query

app = FastAPI()


@app.get("/items/")
async def read_items(
    hidden_query: Union[str, None] = Query(default=None, include_in_schema=False),
):
    if hidden_query:
        return {"hidden_query": hidden_query}
    else:
        return {"hidden_query": "Not found"}

自定义验证¶

有些情况下，你可能需要进行一些自定义验证，而这些验证无法通过上述参数完成。

在这些情况下，你可以使用一个自定义验证函数，该函数在常规验证之后应用（例如在验证值为 str 之后）。

你可以使用 Pydantic 的 AfterValidator 在 Annotated 中实现这一点。

Tip

Pydantic 还有 BeforeValidator 和其他验证器。🤓

例如，这个自定义验证器检查项目 ID 是否以 isbn- 开头（表示 ISBN 书号）或以 imdb- 开头（表示 IMDB 电影 URL ID）：

Python 3.10+

import random
from typing import Annotated

from fastapi import FastAPI
from pydantic import AfterValidator

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[str | None, AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

🤓 Other versions and variants

Python 3.9+Python 3.8+

import random
from typing import Annotated, Union

from fastapi import FastAPI
from pydantic import AfterValidator

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[Union[str, None], AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

import random
from typing import Union

from fastapi import FastAPI
from pydantic import AfterValidator
from typing_extensions import Annotated

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[Union[str, None], AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

Info

这需要 Pydantic 版本 2 或更高版本。😎

Tip

如果你需要进行任何需要与外部组件（如数据库或其他 API）通信的验证，你应该改用 FastAPI 依赖项，你将在后面学习它们。

这些自定义验证器适用于仅使用请求中提供的相同数据进行检查的情况。

理解这段代码¶

关键点只是在 Annotated 中使用AfterValidator 和一个函数。如果你不感兴趣，可以跳过这部分。🤸

但如果你对这个特定的代码示例感兴趣并且仍然有兴趣，这里有一些额外的细节。

使用 `value.startswith()` 的字符串¶

你注意到了吗？使用 value.startswith() 的字符串可以接受一个元组，它会检查元组中的每个值：

Python 3.10+

# Code above omitted 👆

def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id

# Code below omitted 👇

👀 Full file preview

Python 3.10+

import random
from typing import Annotated

from fastapi import FastAPI
from pydantic import AfterValidator

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[str | None, AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

🤓 Other versions and variants

Python 3.9+Python 3.8+

import random
from typing import Annotated, Union

from fastapi import FastAPI
from pydantic import AfterValidator

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[Union[str, None], AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

import random
from typing import Union

from fastapi import FastAPI
from pydantic import AfterValidator
from typing_extensions import Annotated

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[Union[str, None], AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

随机项目¶

通过 data.items()，我们得到一个可迭代对象，其中包含每个字典项的键和值的元组。

我们使用 list(data.items()) 将这个可迭代对象转换为一个真正的 list。

然后使用 random.choice() 从列表中获取一个随机值，因此我们得到一个 (id, name) 的元组。它可能类似于 ("imdb-tt0371724", "The Hitchhiker's Guide to the Galaxy")。

然后我们将元组的这两个值赋值给变量 id 和 name。

因此，如果用户没有提供项目 ID，他们仍然会收到一个随机建议。

...我们在一行简单的代码中完成了所有这些。🤯 你不喜欢 Python 吗？🐍

Python 3.10+

# Code above omitted 👆

@app.get("/items/")
async def read_items(
    id: Annotated[str | None, AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

👀 Full file preview

Python 3.10+

import random
from typing import Annotated

from fastapi import FastAPI
from pydantic import AfterValidator

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[str | None, AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

🤓 Other versions and variants

Python 3.9+Python 3.8+

import random
from typing import Annotated, Union

from fastapi import FastAPI
from pydantic import AfterValidator

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[Union[str, None], AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

import random
from typing import Union

from fastapi import FastAPI
from pydantic import AfterValidator
from typing_extensions import Annotated

app = FastAPI()

data = {
    "isbn-9781529046137": "The Hitchhiker's Guide to the Galaxy",
    "imdb-tt0371724": "The Hitchhiker's Guide to the Galaxy",
    "isbn-9781439512982": "Isaac Asimov: The Complete Stories, Vol. 2",
}


def check_valid_id(id: str):
    if not id.startswith(("isbn-", "imdb-")):
        raise ValueError('Invalid ID format, it must start with "isbn-" or "imdb-"')
    return id


@app.get("/items/")
async def read_items(
    id: Annotated[Union[str, None], AfterValidator(check_valid_id)] = None,
):
    if id:
        item = data.get(id)
    else:
        id, item = random.choice(list(data.items()))
    return {"id": id, "name": item}

总结¶

你可以为参数声明额外的验证和元数据。

通用验证和元数据：

alias
title
description
deprecated

特定于字符串的验证：

min_length
max_length
pattern

使用 AfterValidator 进行自定义验证。

在这些示例中，你看到了如何为 str 值声明验证。

请参阅下一章，了解如何为其他类型（如数字）声明验证。

查询参数与字符串验证¶

额外验证¶

导入 Query 和 Annotated¶

在 q 参数的类型中使用 Annotated¶

在 q 参数中将 Query 添加到 Annotated¶

替代方案（旧）：将 Query 作为默认值¶

将 Query 作为默认值或在 Annotated 中¶

Annotated 的优势¶

添加更多验证¶

添加正则表达式¶

Pydantic v1 的 regex 而非 pattern¶

默认值¶

必需参数¶

必需但可以是 None¶

查询参数列表 / 多值¶

带默认值的查询参数列表 / 多值¶

仅使用 list¶

声明更多元数据¶

别名参数¶

弃用参数¶

从 OpenAPI 中排除参数¶

自定义验证¶

理解这段代码¶

使用 value.startswith() 的字符串¶

随机项目¶

总结¶

导入 `Query` 和 `Annotated`¶

在 `q` 参数的类型中使用 `Annotated`¶

在 `q` 参数中将 `Query` 添加到 `Annotated`¶

替代方案（旧）：将 `Query` 作为默认值¶

将 `Query` 作为默认值或在 `Annotated` 中¶

`Annotated` 的优势¶

Pydantic v1 的 `regex` 而非 `pattern`¶

必需但可以是 `None`¶

仅使用 `list`¶

使用 `value.startswith()` 的字符串¶