Question

我有一个observable，它监视一个被动表单上的值更改，然后根据值更改来调查一个新查询

// this need to run like this...on accountId.value changes if id is > 0 , otherwise accountMessagesDataSource$ = []
this.accountMessagesDataSource$ = this.piForm.get('accountId').valueChanges.pipe(
    switchMap(query => this.pitching.getAccountMessage(query)),
    tap(accountMessages => this.accountMessages = accountMessages)).subscribe();

我需要这样有条件地运行，如上面的评论专栏所述...

Answer 1

所以你只想在getAccountMessage时运行id > 0，否则只返回一个空数组：

this.accountMessagesDataSource$ = this.piForm.get('accountId').valueChanges
  .pipe(
    switchMap(id => id > 0
      ? this.pitching.getAccountMessage(id)
      : of([])
    ),
    tap(accountMessages => this.accountMessages = accountMessages),
  )
  .subscribe();

Answer 2

您可以使用flatMap撰写您的信息流

this.accountMessagesDataSource$ = this.piForm.get('accountId').valueChanges.flatMap((id)=> id > 0 ? this.pitching.getAccountMessage(id):of([]))

rxjs条件可观察的反应形式valueChanges

2 个答案: