将 4 个 observable 与条件合并

Question

我需要创建一个 Observable 来收集来自一些 http 请求的其他 observable。新的 observable 必须是相同对象类型的集合，但每个项目必须是唯一的。你能帮我写出正确的方法来实现这个目标吗？

// The result observable that I need
topicCollection$ = BehaviorSubject<Topic[]> = new BehaviorSubject<Topic[]>(null);

// Boolean observable of authentication
isAuthenticated: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(null);

// Return default topic
get defaultTopics$(): Observable<Topic[]>{
   return this.defaultTopic.asObservable();
}

// Return topics selected by Admin
get TopTopics$(): Observable<Topic[]>{
  return this.topTopic.asObservable();
}

//Return topics selected by User
get userTopics$: Observable<Topic[]>{
   return this.userTopic.asObservable();
}

//Return user settings 
get userSettings$(): Observable<any[]>{
  return this.userSettings.asObservable();
}

所以约束是：

1. 如果用户未登录，集合必须按此顺序：defaultTopic、topTopic
2. 如果用户登录，集合必须按以下顺序：defaultTopic、topTopic、userTopic
3. 如果用户已登录，我将读取过滤默认主题的 UserSettings$（如果它们将被隐藏或显示）
4. 主题必须是唯一的（重复的主题仅在默认情况下且用户主题可观察）

我尝试使用 combineLatest 和 forkJoin，但我不知道如何区分操作员和身份验证观察者。

Answer 1

你可以试试这样的。当然，由于您的问题不完整，所以这个答案也不完整。

您必须自己实现一些部分。不过，下面应该是一个不错的开始修补的地方。

get topicCollection$(): Observable<Topic[]> {

  return this.isAuthenticated.pipe(
    take(1),
    switchMap(isLogged => {

      // The easy part, merge arrays emitted from two separate streams
      const mergeDefaultTop$ = forkJoin([
        this.defaultTopics$.pipe(take(1)),
        this.topTopics$.pipe(take(1))
      ]).pipe(
        map((v: Topic[][]) => v.flat())
      );

      // If the user is logged in, merge then filter the merged topics.
      return !isLogged ? mergeDefaultTop$ : mergeDefaultTop$.pipe(
        switchMap(topics => this.userTopics$.pipe(
          map(userTopics => [...topics, ...userTopics])
        )),
        switchMap(topics => this.userSettings$.pipe(
          map(settings => topics
            // You'll want to update this filter. I can't define it for you 
            // as I dont know what a topic is/ how it's labled, etc.
            .filter(topic => topic !in settings)
            // Filter to remove duplicats. You may want to better define
            // equality depending on your use case (again, I can't do
            // that for you with what you've provided)
            .filter((value, index, self) =>
              self.indexOf(value) === index
            )
          )
        ))
      );

    })
  );

}