高级依赖项

参数化依赖项

我们目前所见的依赖项都是固定函数或类。

但有些情况下，你可能希望能够为依赖项设置参数，而无需声明多个不同的函数或类。

假设我们想要一个依赖项，用于检查查询参数 q 是否包含某些固定内容。

但我们希望能够参数化该固定内容。

可调用实例

在 Python 中，有一种方法可以让类的实例成为“可调用对象”。

不是类本身（它已经是可调用的），而是该类的实例。

为此，我们声明一个 __call__ 方法：

Python 3.9+

from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import Depends, FastAPI
from typing_extensions import Annotated

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

Tip

Prefer to use the Annotated version if possible.

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: bool = Depends(checker)):
    return {"fixed_content_in_query": fixed_content_included}

在这种情况下，FastAPI 将使用这个 __call__ 方法来检查额外参数和子依赖项，并且之后会调用它来为路径操作函数中的参数传递值。

参数化实例

现在，我们可以使用 __init__ 来声明实例的参数，以便对依赖项进行“参数化”：

Python 3.9+

from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import Depends, FastAPI
from typing_extensions import Annotated

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

Tip

Prefer to use the Annotated version if possible.

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: bool = Depends(checker)):
    return {"fixed_content_in_query": fixed_content_included}

在这种情况下，FastAPI 不会触及或关心 __init__，我们将直接在代码中使用它。

创建实例

我们可以这样创建该类的实例：

Python 3.9+

from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import Depends, FastAPI
from typing_extensions import Annotated

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

Tip

Prefer to use the Annotated version if possible.

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: bool = Depends(checker)):
    return {"fixed_content_in_query": fixed_content_included}

这样我们就能够“参数化”依赖项，现在它内部包含了 "bar"，作为属性 checker.fixed_content。

将实例用作依赖项

然后，我们可以在 Depends(checker) 中使用这个 checker，而不是 Depends(FixedContentQueryChecker)，因为依赖项是实例 checker，而不是类本身。

在解析依赖项时，FastAPI 会这样调用 checker：

checker(q="somequery")

……并将其返回的任何内容作为依赖项的值传递给路径操作函数中的参数 fixed_content_included：

Python 3.9+

from typing import Annotated

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

🤓 Other versions and variants

Python 3.8+Python 3.8+ - non-Annotated

from fastapi import Depends, FastAPI
from typing_extensions import Annotated

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: Annotated[bool, Depends(checker)]):
    return {"fixed_content_in_query": fixed_content_included}

Tip

Prefer to use the Annotated version if possible.

from fastapi import Depends, FastAPI

app = FastAPI()


class FixedContentQueryChecker:
    def __init__(self, fixed_content: str):
        self.fixed_content = fixed_content

    def __call__(self, q: str = ""):
        if q:
            return self.fixed_content in q
        return False


checker = FixedContentQueryChecker("bar")


@app.get("/query-checker/")
async def read_query_check(fixed_content_included: bool = Depends(checker)):
    return {"fixed_content_in_query": fixed_content_included}

Tip

这一切可能看起来有些刻意。而且目前可能还不清楚它有多大用处。

这些示例故意保持简单，但展示了其工作原理。

在关于安全的章节中，有一些实用函数也是以相同方式实现的。

如果你理解了所有这些，你就已经了解了那些安全实用工具在底层的工作原理。