* <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/X-Forwarded-Proto" class="external-link" target="_blank">X-Forwarded-Proto</a>
* <a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/X-Forwarded-Host" class="external-link" target="_blank">X-Forwarded-Host</a>

///

/// note | 技术细节

任何一个可以与以下内容一起使用的函数：

* <a href="https://docs.python.org/3/library/contextlib.html#contextlib.contextmanager" class="external-link" target="_blank">`@contextlib.contextmanager`</a> 或者
* <a href="https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager" class="external-link" target="_blank">`@contextlib.asynccontextmanager`</a>

都可以作为 **FastAPI** 的依赖项。

实际上，FastAPI内部就使用了这两个装饰器。

///

## 使用 `yield` 的数据库依赖项

Aqui veremos um exemplo usando <a href="https://sqlmodel.tiangolo.com/" class="external-link" target="_blank">SQLModel</a>.

**SQLModel** é construído sobre <a href="https://www.sqlalchemy.org/" class="external-link" target="_blank">SQLAlchemy</a> e Pydantic. Ele foi criado pelo mesmo autor do **FastAPI** para ser o par perfeito para aplicações **FastAPI** que precisam usar **bancos de dados SQL**.

    # o targetLanguage: (Required)
    #  The target language.
    #  Your possible choices are:
    #
    #       java, csharp, scala
    #
    ; targetLanguage = java
    # - - - - - - - - - -/

    # /- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    # o targetContainer: (Required)
    #  The target DI container.
    #  Your possible choices are:
    #

    /**
     * Parses a sequence of XML elements and converts them to the given target type.
     *
     * @param parser The XML parser
     * @param toType The target type
     * @return Converted instance of the target type
     */
    private Object parse(final MXParser parser, final TypeLiteral<?> toType) throws Exception {

Aber in realen Fällen würden Sie bei der Implementierung von Sicherheit mehr Vorteile durch die Verwendung der integrierten [Sicherheits-Werkzeuge (siehe nächstes Kapitel)](../security/index.md){.internal-link target=_blank} erzielen.

///

## Abhängigkeitsfehler und -Rückgabewerte { #dependencies-errors-and-return-values }

Sie können dieselben Abhängigkeits-*Funktionen* verwenden, die Sie normalerweise verwenden.

import static java.lang.annotation.RetentionPolicy.CLASS;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns

import static java.lang.annotation.RetentionPolicy.CLASS;

import com.google.common.annotations.GwtCompatible;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

/**
 * Annotates a "top-level" type-variable usage that takes its nullness from the type argument
 * supplied by the user of the class. For example, {@code Multiset.Entry.getElement()} returns

## Conclusión { #conclusion }

Con esto deberías tener una comprensión básica de qué son las **variables de entorno** y cómo usarlas en Python.

También puedes leer más sobre ellas en la <a href="https://en.wikipedia.org/wiki/Environment_variable" class="external-link" target="_blank">Wikipedia para Variable de Entorno</a>.

    * `Path()`
    * `Query()`
    * `Header()`
    * `Cookie()`