javascript - 如何让两个promise同步执行？

Question

这个问题已经有答案了:

Using async/await with a forEach loop (33 个回答)

已关闭 3 年前。

我正在尝试从 Redis 获取一些数据，用它做一些事情，然后将其存储回来。所以我有两次对redis的调用:

_.each(guids, async (guid) => {
            const targetRecordSl = await this.redisConn.ft_searchAsync(this.TargetIndex, [`@guid:{${guid}}`, 'RETURN', 1, 'sl']);
            console.log('Trying to add sl:' + slId + ' to: '+guid+ ' existing value:'+ targetRecordSl[2][1]);
            let sl = '';
            if(targetRecordSl[2][1] != '_null' && !targetRecordSl[2][1].includes(slId)) {
                sl = targetRecordSl[2][1] + ', ' + slId;
            } else {
                sl = slId;
            }
            const response = await this.redisConn.ft_addAsync(this.TargetIndex, [`${this.TargetIndex}:${guid}`, 1, 'REPLACE', 'PARTIAL', 'FIELDS', 'sl', sl]);
            console.log(response);

第一个查询执行循环的所有迭代，而不等待第二个查询完成:

Trying to add sl:11 to: P6d43d914bea8b91ece2a0a3c081b9b85 existing value:10
Trying to add sl:10 to: P6d43d914bea8b91ece2a0a3c081b9b85 existing value:10
Trying to add sl:9 to: P24e58b30a0658b8f0e5f9ce1ca0acc1f existing value:9
Trying to add sl:8 to: P7345d54686bfd491747eefd4e05d0362 existing value:8
OK
OK
OK
OK

这不是我想要的。我希望一个 promise 等待另一个完成:

Trying to add sl:11 to: P6d43d914bea8b91ece2a0a3c081b9b85 existing value:10
OK
Trying to add sl:10 to: P6d43d914bea8b91ece2a0a3c081b9b85 existing value:10
OK
Trying to add sl:9 to: P24e58b30a0658b8f0e5f9ce1ca0acc1f existing value:9
OK
Trying to add sl:8 to: P7345d54686bfd491747eefd4e05d0362 existing value:8
OK

请多多指教。

Answer 1

也许你可以尝试用普通的 for 循环来做到这一点:

for (const guid of guids) {
  const targetRecordSl = await this.redisConn.ft_searchAsync(this.TargetIndex, [`@guid:{${guid}}`, 'RETURN', 1, 'sl']);

  console.log('Trying to add sl:' + slId + ' to: ' + guid + ' existing value:' + targetRecordSl[2][1]);

  let sl = '';
  if (targetRecordSl[2][1] != '_null' && !targetRecordSl[2][1].includes(slId)) {
    sl = targetRecordSl[2][1] + ', ' + slId;
  } else {
    sl = slId;
  }

  const response = await this.redisConn.ft_addAsync(this.TargetIndex, [`${this.TargetIndex}:${guid}`, 1, 'REPLACE', 'PARTIAL', 'FIELDS', 'sl', sl]);

  console.log(response);
}

如果这是顶级代码，您可以尝试:

async function processGuids(guids) {
    for (const guid of guids) {
        const targetRecordSl = await this.redisConn.ft_searchAsync(this.TargetIndex, [`@guid:{${guid}}`, 'RETURN', 1, 'sl']);

        console.log('Trying to add sl:' + slId + ' to: ' + guid + ' existing value:' + targetRecordSl[2][1]);

        let sl = '';
        if (targetRecordSl[2][1] != '_null' && !targetRecordSl[2][1].includes(slId)) {
            sl = targetRecordSl[2][1] + ', ' + slId;
        } else {
            sl = slId;
        }

        const response = await this.redisConn.ft_addAsync(this.TargetIndex, [`${this.TargetIndex}:${guid}`, 1, 'REPLACE', 'PARTIAL', 'FIELDS', 'sl', sl]);

        console.log(response);
    }
}

processGuids(guids)
    .then(() => {
        console.log('JOB DONE!!')
        // Here goes your following code (if it has to be executed after processing all guids)
    });