angular 4-如何重写嵌套订阅 [英] angular 4 - How to rewrite nested subscription

问题描述

我有一个嵌套订阅，我认为这不是一个好习惯，尽管它通常对我有用，但在某些情况下可能会给我带来麻烦.

I have a nested subscription which I believe is not good practice, and even though it usually works for me, in one instance it might causing me a problem.

我该如何重写以下内容，使其不嵌套订阅?

How could I rewrite the following so it is not nested subscription?

this.pagesService.postReorderPages(ids).subscribe(res => {
                    if (res === "ok") {
                        console.log(res);
                        this.pagesService.getPages().subscribe(pages => {
                            this.pagesService.pagesBS.next(pages);
                            console.log(pages);
                        });
                    }
                });

推荐答案

我始终建议人们尽力将 logic 保留在自己的信息流中，并将 effects 保留在订阅中或.do()回调.因此，我认为您避免嵌套订阅的本能是正确的.

I always recommend that people do their best to keep logic in their stream, and effects inside subscriptions or .do() callbacks. So i think your instincts about avoiding nested subscriptions are on point.

this.pagesService.postReorderPages( ids )
    .filter( res => res === 'ok' ) // moved logic from your subscription to stream
    .mergeMap( () => this.pagesService.getPages() )
    .subscribe( pages => {
        this.pagesService.pagesBS( pages );
    });

如果您发现自己想避免嵌套订阅，那么通常您想联系*Map运算符之一.

If you find yourself trying to avoid a nested subscription, oftentimes you want to reach for one of the *Map operators.

在rxjs中，有四个

1. mergeMap
2. concatMap
3. switchMap
4. exhaustMap

1. mergeMap
2. concatMap
3. switchMap
4. exhaustMap

它们的行为都有些不同，所以我不能保证这将完美地实现您的功能.但是它们都具有相同的签名，并且它们的存在是为了处理混乱"的嵌套订阅(在某些库中有时也称为高阶"或元"流).

They all behave a little differently, so I can't guarantee that this will implement your feature perfectly. But they all have the same signature, and they exist to handle "messy" nested subscribes (also sometimes referred to as "higher-order" or "meta" streams, in some libraries).

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