RXJS 重复查询直到满足条件? [英] RXJS Repeat query until a condition is met?

问题描述

我使用的 API 只返回有限数量的结果，比如 100.

I'm using an API that returns only a limited number of results, say 100.

我想重复一个查询，直到返回结果集为 <100 这意味着我得到了最后的结果.

I'd like to repeat a query until the return result set is < 100 which would mean I've got the last result.

所以它会是这样的:

1. 进行查询
2. 结果集是否小于限制?如果是，请再次执行并附加结果.
3. 一旦结果集小于限制，发出最终结果.

推荐答案

您可以使用 expand 运算符来实现简单的条件重复"行为.

You can use the expand operator for a simple "conditional repeat" behavior.

仅作为示例，我将查询更改为返回一个数字，而不是结果集.下面继续查询，直到检索到的数小于100

Just for the example, instead of a result set I changed the query to return a number. The following keep querying until the retrieved number is less than 100

const { defer, empty } = rxjs;
const { expand, toArray} = rxjs.operators;

const query$ = defer(async () =>  Math.floor(Math.random()*1000));
   
query$
  .pipe(
    expand(result => result < 100 ? empty() : query$),
    toArray()
  )
  .subscribe(console.log);

<script src="https://unpkg.com/rxjs/bundles/rxjs.umd.min.js"></script>

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