如何在返回外部可观察对象之前修改可观察对象发出的每个对象的内部元素

Question

我对 Observables 和 rxjs 的整个概念很陌生，所以这可能非常明显。但是请帮忙，因为我很想学习

当用户在博客文章下点击显示 cmets 时，我有一个功能

 showComments(){
    
    this.firestoreservice.getComments(this.job.id).subscribe( data =>{
      this.comments = data //type [] of comment objects with (message,posterID,timeposted...)
    })

    this._showcomments = true;

  }

此函数调用一个服务函数，该函数将一个可观察对象返回到该作业的我的 cmets 列表中。 在订阅那个 observable 时初始化一个变量来保存我所有的 cmets。 但是，在我这样做之前，有没有办法用匹配的用户名替换每个评论的 posterID 属性？请参阅下面的预期结果：

showComments(){
   
   this.firestoreservice.getComments(this.job.id).subscribe( data =>{

     //for each comment held in data, replace comment.posterID with getUserName(posterID)
     //getUserName(posterID) will also return an observable which emmits one string
     //then append comment to comments list (or add back in to data then destructively assign 
     //comments=data )
     
     this.comments = data //type [] of comment objects with (message,posterID,timeposted...)
   })

   this._showcomments = true;

 }

Answer 1

它看起来有点像这样......

this.firestoreservice.getComments(this.job.id).pipe(
  switchMap(comments => { // switchMap to subscribe to inner
    const getUsers$ = comments.map(comment => // array map comments into userName fetch
      this.firestoreservice.getUserName(comment.posterID).pipe(
        // once you have the username, rx map back into the comment with the username assigned
        map(userName => ({...comment, posterID: userName})),
        first() // use to complete after one emission to make forkJoin work
      )
    )
    return forkJoin(...getUsers$); // forkJoin them all together for parallel execution
  });
).subscribe(data => {
  this.comments = data // now just set the data
})