如何在RxJS中处理循环依赖的可观察变量? [英] How to handle circularly dependent observables in RxJS?

问题描述

比如说在服务器上的某个位置之间存在一个映射 整数和名称，网页在用户提供简单输入的地方 可以输入一个数字并为其指定相应的名称.

Let's say e.g. that somewhere on a server there is a mapping between integers and names and a web page provides a simple input where a user can enter a number and is given the corresponding name.

从根本上讲，这个问题很简单:

In its basic form, this problem is simple:

const input$          = Rx.Observable.fromEvent(..., "input");
const request$        = input$.map( ... );
const serverResponse$ = request$.flatMap( askServer );

现在，我想缓存结果，以便仅请求 当号码不在缓存中时完成.

Now I would like to cache the results so that a request is only done when the number is not in the cache.

const input$          = Rx.Observable.fromEvent(..., "input");
// request$ should now also depend on cache$
const request$        = ???;
const serverResponse$ = request$.flatMap( askServer );
const cache$          = serverResponse$.scan( ... );

但是现在request$取决于cache$，而cache$取决于serverResponse$ 反过来取决于request$.

But now request$ depends on cache$ which depends on a serverResponse$ which in turn depends on request$.

我该如何解决这个问题?

How do I solve this problem?

推荐答案

在依赖图中的循环中的某个时刻引入Subject作为代理，然后将实际的Observable(cache$)的行为镜像到代理主题(proxyCache$).

Introduce a Subject as a proxy at some point in the cycle in the dependency graph, then mirror the behavior of the real Observable (cache$) onto the proxy Subject (proxyCache$).

const input$          = Rx.Observable.fromEvent(..., "input");
const proxyCache$     = new Rx.Subject();
const request$        = input$.merge(proxyCache$).map( ... );
const serverResponse$ = request$.flatMap( askServer );
const cache$          = serverResponse$.scan( ... );
cache$.subscribe(proxyCache$);

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