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如何将mongoose查询的结果保存到变量中

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我试图通过循环播放专辑中的歌曲列表，查找相关歌曲并尝试保存到阵列中供以后使用，将一些对象保存到数组中 . 有没有办法实现这个目标？

我需要一些使用猫鼬的解释 .

exports.playlistPlayer = function (req, res, next) {
Playlist.findById({
    _id: req.body.playlist._id
}, (err, playlist) => {

    var customAlbum = []; //This variable it's inside the same block i believe


    playlist.songs.forEach(function (song) {
        Song.findById({
            _id: song.song_id
        }, (err, songs) => {

            var customSong = {
                title: songs.title,
                time: songs.time,
                source: songs.source,
                song_id: songs._id
            }
            customAlbum.push(customSong)
            console.log(customAlbum) //it works here
        });

    });

    console.log(customAlbum) //it returns an empty array here where i need the data

 });
};
javascript arrays node.js mongodb mongoose

1 回答

  • 0

    问题是 findById 方法也是异步的 . 我建议你在javascript中学习promises . 一种可能的解决方案是使用ES7的async / await功能：

    // asynchronous function
exports.playlistPlayer = async (req, res, next) => {
  // wait for the findById method promise to resolve
  const playlist = await Playlist.findById({
    _id: req.body.playlist._id
  })

  // wait for finding all songs in db whose id's are in
  // the playlist.songs array
  const songs = await Song.find({
    _id: { $in: playlist.songs }
  })

  // create the customAlbum by using the map method to
  // tramsform the song objects to the required form
  const customAlbum = songs.map(song => ({
    title: song.title,
    time: song.time,
    source: song.source,
    song_id: song._id
  }))

  // and there you should now have your customAlbum array
  console.log(customAlbum)

  // now you can use it for example
  // to return a response to the client:
  // res.json(customAlbum)
}
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