错误不能读取属性“跟踪”空的（node.js的）

Question

我试图创建曲目的专辑，但我被困在一个错误

这是我的路线代码

// Adding track to album 
router.get('/:album_id/track/new', function(req, res){ 
    Album.findById(req.params.album_id, function(err, falbum){ 
     if(err){ 
      console.log(err); 
     } else { 
      res.render('tracks/add', {albums: falbum}); 
     } 
    }); 
}); 

// Post routes 
router.post('/:album_id/track',upload.single('songs'), function(req, res){ 
    Album.findById(req.params.album_id, function(err, album){ 
     if(err){ 
      console.log(err); 
     } else { 
      if(req.file){ 
       console.log('Uploading Song ....'); 
       var songs = req.file.filename; 
      } else { 
       console.log('No Song Uploaded...'); 
      } 
      var songname = req.body.songname; 
      var songs = songs; 
      var newSong = {songname: songname, songs:songs}; 

      Track.create(newSong, function(err, track){ 
       if(err){ 
        console.log(err); 
       } else { 
        track.albumId.id = req.params.album_id; 
        track.save(); 
        album.tracks.push(track); 
        album.save(); 
        console.log('New Track is created'); 
        res.redirect('/albums/' + album._id); 
       } 
      }); 
     } 
    }); 
}); 

router.get('/:album_id',function(req, res){ 
    Album.findById(req.params.album_id).populate('tracks').exec(function(err, album){ 
     if(err){ 
      console.log(err); 
     } else { 
      res.render('albums/show', {albums: album}) 
     } 
    }); 
}); 



module.exports = router; 

我得到以下错误

v4\node_modules\mongoose\node_modules\mongodb\lib\utils.js:98 
    process.nextTick(function() { throw err; }); 
           ^

TypeError: Cannot read property 'tracks' of null 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\routes\albums.js:53:11 
    at Function.<anonymous> (C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\lib\model.js:3324:16) 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\lib\model.js:1870:14 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\async\lib\async.js:726:13 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\async\lib\async.js:52:16 
    at done (C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\async\lib\async.js:246:17) 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\async\lib\async.js:44:16 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\async\lib\async.js:723:17 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\async\lib\async.js:167:37 
    at model.callbackWrapper (C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\lib\model.js:1843:11) 
    at next_ (C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\hooks-fixed\hooks.js:89:34) 
    at fnWrapper (C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\hooks-fixed\hooks.js:186:8) 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\lib\model.js:3324:16 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\lib\model.js:228:5 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\lib\model.js:135:7 
    at C:\Users\tjesu\Desktop\pidal\pidal-v4\node_modules\mongoose\node_modules\mongodb\lib\collection.js:504:5 

我该怎么办？这个错误呢？ 我试图改变曲目来跟踪，但我仍然有错误 谢谢！

Answer 1

您能验证Album.findById是否返回album？

看起来您的数据库查询与任何文档都不匹配，因此album未定义，因此您无法访问文档上的曲目属性。

Answer 2

我认为在track被成功创建后，你在pushing tracksalbums文件中犯了错误。

你应该推track._id代替track。（我可以看到你正在试图pupulate的曲目，所以你必须在你的schema使用ObjectId和reference）。

当您推动整个trackdocument,album可能无法成功保存。由于没有附加回调（album.save()），因此不会显示实际的error。因此，没有album文件被创建，它是当您使用album.findById

这是给null为什么它显示在使用populate('tracks')你这个错误：cannot read property tracks of null.

Track.create(newSong, function(err, track){ 
      if(err){ 
       console.log(err); 
      } else { 
       track.albumId.id = req.params.album_id; 
       track.save(); 
       album.tracks.push(track._id);//Here _id should be pushed. 
       album.save(); 
       console.log('New Track is created'); 
       res.redirect('/albums/' + album._id); 
      } 
     });