获取数据后如何使该变量执行？ [复制]

Question

我不知道问题出在哪里，我知道标题没有描述我对此的任何看法。 这是我面临的问题。 我目前正在使用 MERN 应用程序。

我有一条快递路线，我从两个表中请求数据库中的一些数据。

playlist.post("/getplaylistSongs", (req, res) => {
  const { cookie } = req.body;
  const sql = "SELECT * FROM playlist WHERE user_id = ?";
  dbCon.query(sql, [cookie], (err, result) => {
    if (err) {
      res.status(400).json({
        message: "failed to get playlist details ",
      });
    } else {
      let playlistSongs = [];
      result.forEach((element, index) => {
        const audio_id = element.audio_id;
        dbCon.query(
          "SELECT * FROM audios where video_id = ?",
          [audio_id],
          (err, song) => {
            if (err) {
              res.status(400).json({
                message: "failed to get music",
              });
            } else {
              playlistSongs.push(song);
            }
          });
      });
     console.log(playlistSongs); 

      res.status(200).json({
        playlist: playlistSongs,
      });
    }
  });
});

但是这里的问题是我尝试这样做我总是将playlistSongs 作为一个空数组。 谢谢你。评论以纠正问题。

编辑：现在我知道问题与 javascript 的执行有关。

Answer 1

试试async / await:

playlist.post('/getplaylistSongs', async (req, res) => {
  const { cookie } = req.body;
  const sql = 'SELECT * FROM playlist WHERE user_id = ?';
  try {
    const result = await dbCon.query(sql, [cookie]);

    let playlistSongs = [];
    result.forEach(async (element, index) => {
      const audio_id = element.audio_id;
      const song = await dbCon.query(
        'SELECT * FROM audios where video_id = ?',
        [audio_id]
      );
      playlistSongs.push(song);
    });
    console.log(playlistSongs);

    res.status(200).json({
      playlist: playlistSongs,
    });
  } catch (e) {
    res.status(400).json({
      message: 'failed to get playlist details ',
    });
  }
});