基于条件的RXJS条件switchMap [英] Rxjs conditional switchMap based on a condition

问题描述

我遇到以下情况:

myObservable1.pipe(
  switchMap((result1: MyObservable1) => {
    if (condition) {
      return myObservable2;
    } else {
      return of(null);
    }
  })
).subscribe(myObservable1 | myObservable2) => {

因此，如果条件为false，我只需要执行一个请求，如果条件为true，则必须将第一个请求链接到下一个请求，它们实质上是对服务器api的两个请求.

So if condition is false I only have to perform one request, if the condition is true, I have to chain the first request to the following one, they are essentially two requests to the server api.

是否有更好的解决方案而不返回该 null ?
RxJ中是否有条件运算符?

Is there a better solution without returning that null?
Is there any conditional operator in RxJs?

谢谢！

推荐答案

另一种可能性是在SwitchMap中使用运算符iif.

Another possibility is to use the operator iif in a SwitchMap.

https://www.learnrxjs.io/learn-rxjs/operators/有条件的/iif

https://rxjs-dev.firebaseapp.com/api/index/函数/iif

但是它可以限制控制特定功能的可能性可观察条件:

but it can restrain the possibility to control specfic conditions on your Observable :

myObservable1
.pipe( 
      switchMap(result1 =>
               iif(() => condition
               , myObservable2
               , myObservable1
            )
      )
.subscribe(result => console.log(result)); 

您可以在其中用返回布尔值的函数替换"condition".具有功能:

Where you can replace 'condition' by a function returning a boolean. With a function :

myObservable1
    .pipe( 
          switchMap(result1 =>
                   iif(() => test(result1)
                   , myObservable2
                   , myObservable1
                )
          )
    .subscribe(result => console.log(result)); 

test(result1) : boolean {
     if(result1){
       // the iif() will return myObservable2
       return true;
     }else{
       /: the iif() will return myObservable1
       return false ;
     }
}

就像@amjuhire说的那样，您可以使用过滤器和switchMap进行编写:

Like @amjuhire said , you can write with a filter and a switchMap :

myObservable1.pipe(
  filter((result1) => condition)
  switchMap((result1: MyObservable1) => {
    return myObservable2;
  })
).subscribe(result2 => { ... })

给出您的示例的另一种可能性:

Another possibility given your example :

myObservable1.pipe(
  switchMap((result1: MyObservable1) => {
    if (condition) {
      return myObservable2;
    } else {
      return of(result1);
    }
  })
subscribe(result => console.log(result));

或在switchMap中使用EMPTY:

Or using EMPTY in the switchMap :

 myObservable1.pipe(
      switchMap((result1: MyObservable1) => {
        if (condition) {
          return myObservable2;
        } else {
          // Observable that immediately completes
          return EMPTY;
        }
      })
    subscribe(result2 => console.log(result2));

这里的问题是我们不知道您可观察的类型.

The problem here is that we don't know the type in your observable.

所以我无法断定哪种方式更好.

So i can't judge wich way is the better.

这还取决于您如何处理可观察对象的不同调用之间的成功/错误.

It also depends on how you want to handle the success/error between the different calls of your observable.

这篇关于基于条件的RXJS条件switchMap的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！