循环中的数据库查询仅返回一个空数组 [英] Database query in loop returns only an empty array

问题描述

'requestingUserIds'是一个具有不同ID的数组.每个ID都属于用户"表中的一个用户名.这就是为什么我要针对数组"requestingUserIds"中的每个id将对应的用户名循环到数组"requestingUserUsernames"中，并最终将完整的数组(requestingUserUsernames)记录到控制台中.但是，如果我在then函数之外执行此操作，则只会输出一个空数组，可能是我一开始就启动的数组.

'requestingUserIds' is an array, with different ids. Each id belongs to a username in the table 'users'. That's why I want to loop, for each id in the array 'requestingUserIds', the corresponding username into the array 'requestingUserUsernames' and finally log the full array (requestingUserUsernames) into the console. But if I do it outside the then function, only an empty array is output, probably the array I initiated in the beginning.

当我在控制台的then函数中记录数组'requestingUserUsernames'时，每次循环传递都会输出该数组，但是我只想输出最终数组.

When i log the array 'requestingUserUsernames' inside the then function in the console, the array gets outputted for each loop pass, but i only want to output the final array.

requestingUserIds.forEach(userId => {
    db('users')
        .select('username')
        .where({id: userId})
        .then(rows => {
            requestingUserUsernames.push(rows[0].username);
         })
         .catch(error => console.log(error));
});
console.log(requestingUserUsernames);````

推荐答案

尝试一下

const requestingUserUsernames = await Promise.all(requestingUserIds.map(userId =>
    db('users')
        .select('username')
        .where({id: userId})
        .then(rows => rows[0].username)));
console.log(requestingUserUsernames);

确保它在异步功能中

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