Inversify 的分层 DI 如何工作？

Question

inversify-express-utils 自述文件包含以下内容 example on request-scoped services。

我正在尝试为 Koa 应用程序实现类似的东西，但是，我很难理解此示例中的分层 DI 是如何工作的。

import { inject, injectable } from "inversify";
import { BaseHttpController, BaseMiddleware, controller, httpGet } from "inversify-express-utils";
import * as express from "express";

const TYPES = {
    TraceId: Symbol.for("TraceIdValue"),
    TracingMiddleware: Symbol.for("TracingMiddleware"),
    Service: Symbol.for("Service"),
};

@injectable()
class TracingMiddleware extends BaseMiddleware {

    public handler(
        req: express.Request,
        res: express.Response,
        next: express.NextFunction
    ) {
        this.bind<string>(TYPES.TraceIdValue)
            .toConstantValue(`${ req.header('X-Trace-Id') }`);

        next();
    }
}

@controller("/")
class TracingTestController extends BaseHttpController {

    constructor(@inject(TYPES.Service) private readonly service: Service) {
        super();
    }

    @httpGet(
        "/",
        TYPES.TracingMiddleware
    )
    public getTest() {
        return this.service.doSomethingThatRequiresTheTraceID();
    }
}

@injectable()
class Service {
    constructor(@inject(TYPES.TraceIdValue) private readonly traceID: string) {
    }

    public doSomethingThatRequiresTheTraceID() {
        // ...
    }
}

通过阅读文档和代码，我了解到 each Express request handler has a HttpContext attached to it, which in turn has a child DI container attached。

该示例表明 Service class 的 traceID 依赖项已从 Express 请求中附加到 httpContext 的子容器中解析。

但是，我不明白如何确保 traceID 是从子容器而不是父容器或根容器解析的？

Answer 1

magic line of code：

httpContext.container.getNamed<any>(TYPE.Controller, controllerName)[key](...args)

这里是从子容器解析控制器的地方，因此 traceId 依赖项也是从子容器解析的。

Inversify 的分层 DI 如何工作？

How does Inversify's hierarchical DI work?

dependency-injection

express

inversifyjs