db.location.find(){ "_id" : 1, "city_name" : "Delhi", "city" : 1, "country_name" : "India" }{ "_id" : 3, "city_name" : "Pune", "city" : 3, "country_name" : "India" }{ "_id" : 2, "city_name" : "Mumbai", "city" : 2, "country_name" : "India" }{ "_id" : 4, "city_name" : "Chandigarh", "city" : 4, "country_name" : "India" }{ "_id" : 5, "city_name" : "Goa", "city" : 5, "country_name" : "India" }{ "_id" : 6, "city_name" : "Manali", "city" : 6, "country_name" : "India" }這是app.js文件...我嘗試使用它，但它不起作用...我收到此錯(cuò)誤{"name":"MongoError"}var dbo = db.db("mydb");dbo.collection('location').find({}).toArray(function (err, result) {    if (err) {              return res.send(err);              } else               {                return res.send(JSON.stringify(result))                }               })