RXJS：如何在处理流结束时利用发出的 observable？

Question

假设我有一个函数generateIdUpdate，它使用一个可观察的 id 来加载属于该 id 的人的地址。我想在成功完成地址加载后设置一个实例变量来保存选定的 id。最好的方法是什么？

另外，这是否反映了糟糕的设计（即，有一个函数加载地址并在最后更新有状态字段）？

export class TapTest {
  private selectedId: number;
  private id$: Observable<number> = ...;
  
  generateIdUpdate$(): Observable<PersonAddress> {
    return id$.pipe(
      // switchMap in case a new Id is selected while loading
      switchMap(id => loadPerson(id)),
      // Get the observable of addresses
      mergeMap((person: Person) => loadAddresses(person)), 
      tap(
        // since this completed successfully, set the selectedId field to the id
      )
    );
  }

  loadPerson(id: number) : Person { ... }
  loadAddresses(person: Person) : Observable<PersonAddress> { ... }
}

给定以下函数，它尝试获取发出的 id、加载人员、加载地址并返回它们，而且在将地址加载到实例变量时更新人员的有状态 id，正确的方法是什么通过处理流“携带” id？

Answer 1

如果我正确理解您想要做什么，我会以与您所描述的非常相似的方式解决问题，但有一些小的变化（请参阅我的 cmets）

export class TapTest {
  private selectedId: number;
  private id$ = ...;
  
  generateIdUpdate$(): Observable<PersonAddress> {
    return id$.pipe(
      // switchMap in case a new Id is selected while loading
      // loadPerson is a function that returns an Observable and not a function
     // that returns a Person as in your original example
     // otherwise switchMap will not work and actually will not even compile
      switchMap(id => loadPerson(id)),
      // Get the observable of addresses
      // Rather than mergemap I would use concatMap, which basically means
      // "wait until I complete before processing the next notification of my
      // upstream Observable" 
      concatMap((person: Person) => loadAddresses(person)), 
      tap(
        // since this completed successfully, set the selectedId field to the id
        // the tap operator expects a an Observer as input parameter
        // an Observer is an object with 3 properties, next, error and complete
        // each of these property is optional
        // in this case we will define the next property as a function that expexts
        // the notification as input - in pour case we will use the input to set
        // the instance variable selectedId
        {
           next: (id) => this.selectedId = id
        }
      )
    );
  }

  // loadPerson must return an Observable<Person> for the above code to work
  loadPerson(id: number) : Person { ... }

  loadAddresses(person: Person) : Observable<PersonAddress> { ... }
}

无论loadAddress是否成功完成，如果要存储selectedId，可以将tap运算符移到pipe的开头。