确保在发出网络请求之前先发出另一个Observable，但是将响应作为冷的Observable通过重播提供给使用者

分类：编程问答

如何解决确保在发出网络请求之前先发出另一个Observable，但是将响应作为冷的Observable通过重播提供给使用者

我要实现的目标：
我有一个FeaturesService，如果通过提供不同的Promises启用了某些功能，则应该提供信息。
启用的功能列表通过HTTP API作为json对象提供（请参见DataService）。
在发送获取功能列表的HTTP请求之前，我们需要确保首先对用户进行身份验证（请参阅AuthService）。
此外：

  • 仅当某人使用Promises提供的FeaturesService（例如isFeatureXSupported）之一时才发出功能请求，而不必在应用程序启动时或尽快当用户通过身份验证时。 （冷可观察？）
  • HTTP请求的功能只能访问网络一次，之后应进行缓存（重播）

到目前为止，我想出了什么：

import { Subject,Observable,ReplaySubject } from "rxjs";
import { map,shareReplay,switchMap,take } from "rxjs/operators";
import { Container,injectable } from "inversify";
import "reflect-metadata";

interface DtoFeatures {
  supportedFeatures: string[];
}

@injectable()
class AuthService {
  private authenticated$: ReplaySubject<boolean> = new ReplaySubject<boolean>(1);

  public authenticate(): void {
    // Mock code
    console.log("Authenticate Request (Mock) started");
    setTimeout(() => {
      console.log("Authenticate Request (Mock) finished");
      this.authenticated$.next(true);
    },100);
  }

  public isAuthenticated(): Observable<boolean> {
    return this.authenticated$.asObservable();
  }
}

@injectable()
class DataService {
  public getFeatures(): Observable<DtoFeatures> {
    // Mock Code,real HTTP Request happening instead that needs to be authorized
    console.log("Network Request (Mock) started");
    const features$ = new Subject<DtoFeatures>();
    setTimeout(() => {
      console.log("Network Request (Mock) finished");
      features$.next({ supportedFeatures: ["featureX"] });
      features$.complete();
    },150);
    return features$;
  }
}

@injectable()
class FeaturesService {

  // private readonly dtoFeatures: Observable<DtoFeatures> = this.authService.isAuthenticated().pipe(
  //   take(1),//   switchMap(() => this.dataService.getFeatures()),//   shareReplay(1)
  // );

  private readonly dtoFeatures: Observable<DtoFeatures> = this.dataService.getFeatures().pipe(
    shareReplay(1)
  );

  constructor(
    private authService: AuthService,private dataService: DataService
  ) {}

  public supportedFeatures: Promise<string[]> = this.dtoFeatures.pipe(
    map((features) => features.supportedFeatures)
  ).toPromise();

  public isFeatureXSupported: Promise<boolean> = this.supportedFeatures.then(
    (features) => features.some((x) => x === "featureX")
  );

  public isFeatureYSupported: Promise<boolean> = this.supportedFeatures.then(
    (features) => features.some((x) => x === "featureY")
  );
}

@injectable()
class App {
  constructor(
    private authService: AuthService,private featureService: FeaturesService
  ) {
    console.log("App initialized");
    this.authService.authenticate();
    this.featureService.isFeatureXSupported.then((x) => console.log(`FeatureX enabled: ${x}`));
  }
}

// Configure DI
var container = new Container();
container.bind<AuthService>(AuthService).toSelf();
container.bind<DataService>(DataService).toSelf();
container.bind<FeaturesService>(FeaturesService).toSelf();
container.bind<App>(App).toSelf();

// Initialize App
container.resolve(App);

链接到代码框： https://codesandbox.io/s/youthful-cerf-t43mi?file=/src/index.ts

给定的代码涵盖了大多数要求，除了问题外，功能请求是在验证用户之前完成的。

控制台日志：

>Network Request (Mock) started <-- Problem!
>App initialized 
>Authenticate Request (Mock) started 
>Authenticate Request (Mock) finished 
>Network Request (Mock) finished 
>FeatureX enabled: true

因此，我尝试使用此版本，但随后根本没有功能请求：

class FeaturesService {

  private readonly dtoFeatures: Observable<DtoFeatures> = this.authService.isAuthenticated().pipe(
     take(1),switchMap(() => this.dataService.getFeatures()),shareReplay(1)
  );

  // private readonly dtoFeatures: Observable<DtoFeatures> = this.dataService.getFeatures().pipe(
  //   shareReplay(1)
  // );

  ...
}

控制台日志：

>App initialized 
>Authenticate Request (Mock) started 
>Authenticate Request (Mock) finished

我想我在这里混淆了与冷/热可观察物有关的东西，但我无法弄清楚问题所在。我非常感谢您的帮助，我认为这是rxjs / reactive programming的一个很好的现实用例，所以也许其他人也想知道如何实现它。

解决方法

谢谢fridoo！

第一个问题是错误的DI配置，您需要使用.inRequestScope() 或在注册服务时使用.inSingletonScope()，例如：

container.bind<AuthService>(AuthService).toSelf().inRequestScope();

第二个问题是在.toPromise()中使用FeaturesService。即使没有要素服务的使用者，这也导致了网络请求的完成。
通过按可预期的方式一直使用Observables。消费者想要使用异步/等待时也可以使用.toPromise()。

完整代码示例：

import { Subject,Observable,ReplaySubject } from "rxjs";
import { map,shareReplay,switchMap,take } from "rxjs/operators";
import { Container,injectable } from "inversify";
import "reflect-metadata";

interface DtoFeatures {
  supportedFeatures: string[];
}

@injectable()
class AuthService {
  private authenticated$: ReplaySubject<boolean> = new ReplaySubject<boolean>(1);

  public authenticate(): void {
    // Mock code
    console.log("Authenticate Request (Mock) started");
    setTimeout(() => {
      console.log("Authenticate Request (Mock) finished");
      this.authenticated$.next(true);
    },100);
  }

  public isAuthenticated(): Observable<boolean> {
    return this.authenticated$.asObservable();
  }
}

@injectable()
class DataService {
  public getFeatures(): Observable<DtoFeatures> {
    // Mock Code,real HTTP Request happening instead that needs to be authorized
    console.log("Network Request (Mock) started");
    const features$ = new Subject<DtoFeatures>();
    setTimeout(() => {
      console.log("Network Request (Mock) finished");
      features$.next({ supportedFeatures: ["featureX"] });
      features$.complete();
    },150);
    return features$;
  }
}

@injectable()
class FeaturesService {

  private readonly dtoFeatures: Observable<DtoFeatures> = this.authService.isAuthenticated().pipe(
    take(1),switchMap(() => this.dataService.getFeatures()),shareReplay(1)
  );

  constructor(
    private authService: AuthService,private dataService: DataService
  ) {}

  public supportedFeatures: Observable<string[]> = this.dtoFeatures.pipe(
    map((features) => features.supportedFeatures)
  );

  public isFeatureXSupported: Observable<boolean> = this.supportedFeatures.pipe(
    map((features) => features.some((x) => x === "featureX"))
  );

  public isFeatureYSupported: Observable<boolean> = this.supportedFeatures.pipe(
    map((features) => features.some((x) => x === "featureY"))
  );
}

@injectable()
class App {
  constructor(
    private authService: AuthService,private featureService: FeaturesService
  ) {
    console.log("App initialized");
    this.authService.authenticate();

    // Comment this line out,to see that there is no (mocked) network request for features
    this.featureService.isFeatureXSupported.subscribe((x) => console.log(`FeatureX enabled: ${x}`));
    
    // Build promise at consumer level:
    // this.featureService.isFeatureXSupported.toPromise().then((x) => console.log(`FeatureX enabled: ${x}`));
  }
}

// Configure DI
var container = new Container();
container.bind<AuthService>(AuthService).toSelf().inRequestScope();
container.bind<DataService>(DataService).toSelf().inRequestScope();
container.bind<FeaturesService>(FeaturesService).toSelf().inRequestScope();
container.bind<App>(App).toSelf();

// Initialize App
container.resolve(App);

Codesandbox：https://codesandbox.io/s/confident-sammet-z1x2r?file=/src/index.ts

控制台日志（带有使用者）：

>App initialized 
>Authenticate Request (Mock) started 
>Authenticate Request (Mock) finished 
>Network Request (Mock) started 
>Network Request (Mock) finished 
>FeatureX enabled: true

控制台日志（没有使用方）：

>App initialized 
>Authenticate Request (Mock) started 
>Authenticate Request (Mock) finished

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