javascript - 在异步代码的 for 循环完成后，如何解决这个 promise ？

Question

似乎无法弄清楚如何在没有 setTimeout 的情况下完成这项工作。我想仅在异步 PostgreSQL 内容完成并且映射包含应有的所有键/值对后才控制台记录我的映射。

const map = new Map();
pool.query(`SELECT * FROM trips WHERE destination = $1 AND begin_time >= $2 AND begin_time < $3 ORDER BY begin_time`, ['BROWNSVILLE ROCKAWAY AV', '2018-07-18 00:00-04:00', '2018-07-19 00:00-04:00'])
.then(res => {
    return new Promise((resolve, reject) => {
        const { rows } = res;
        resolve(rows);
    });
})
.then(res1 => {
    return new Promise((resolve, reject) => {
        for (let i = 0; i < res1.length; i++) {
            if (res1[i + 1]) {
                pool.query(`SELECT * FROM get_hwtable($1, $2)`, [res1[i].trip_id, res1[i + 1].trip_id]).then(res => {
                    const { rows: hwRows } = res;
                    map.set([res1[i].trip_id, res1[i + 1].trip_id], hwRows);
                }).catch(e => console.log('20', e));
            }
        }
        setTimeout(() => {
            resolve(map);
        }, 8000);
    });
})
.catch(e => console.log('25', e))
.finally(function () {
    console.log(map);
});

Answer 1

您可以简单地对 pool.query 返回的 promise 数组使用 Promise.all

const map = new Map();
pool.query(`SELECT * FROM trips WHERE destination = $1 AND begin_time >= $2 AND begin_time < $3 ORDER BY begin_time`, ['BROWNSVILLE ROCKAWAY AV', '2018-07-18 00:00-04:00', '2018-07-19 00:00-04:00'])
.then(({rows}) => rows)
.then(res1 => Promise.all(res1.map((r, i) => {
    if (res1[i + 1]) {
        return pool.query(`SELECT * FROM get_hwtable($1, $2)`, [r.trip_id, res1[i + 1].trip_id])
        .then(res => {
            const { rows: hwRows } = res;
            map.set([res1[i].trip_id, res1[i + 1].trip_id], hwRows);
        }).catch(e => console.log('20', e))
    }                                 
})))
.catch(e => console.log('25', e))
.finally(function () {
    console.log(map);
});