节点JS返回值未定义

Question

Uri myUri = ....; // initialize Uri here
MediaPlayer mediaPlayer = new MediaPlayer();
mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
mediaPlayer.setDataSource(getApplicationContext(), myUri);
mediaPlayer.prepare();
mediaPlayer.start();

请帮我弄清楚这个问题，它会返回一个未定义的值。我是var ide = req.params.brand_id; gmpro_model.aggregate( {$match: {brand_id: ide}}, {$group: {total_gross:{$sum : "$Gross"}}} ,function(err, results){ console.log(results); }); 的新手。谢谢

Answer 1

来自MongoDb $ group menual https://wiki.saucelabs.com/display/DOCS/Sauce+Connect+Proxy

  

_id字段是强制性的;但是，您可以指定_id值null来计算所有输入文档的累计值。

试试这个

   var ide = req.params.brand_id;
    gmpro_model.aggregate(
        {$match: {brand_id: ide}},
        {$group: {_id:null,total_gross:{$sum : "$Gross"}}}
    ,function(err, results){
    console.log(results);
    });