Question

    var express = require('express');
    var routes = require('./routes');
    var socket = require('socket.io');
    var fs = require('fs');
    var app = module.exports = express.createServer();
    var Server = require('mongodb').Server,
        Db = require('mongodb').Db,
        Connection = require('mongodb').Connection;
    var host = 'localhost';
    var port = Connection.DEFAULT_PORT;
    var db = new Db('node-mongo-examples', new Server(host, port, {}), {native_parser:false});

    db.open(function(err, db) {
        console.log('opened');   
        app.listen(3000); 

    });


    db.collection('locations', function(err, collection) {
          var object= {word:'TEST'};
          collection.insert(object, {safe:true}, function(err, result) {
            var array = collection.findOne({word:'TEST'}, function(err, item) {});            
             console.log(array);// <----always  "undefined" 
          });        
    });

I try to insert the object into the database. And by using “console.log(array)” everytime,I find that it always be “undefined”. Is it can’t be insert into the database or can’t be found from the database. How can I solve it??

But, The ‘console.log(item)’ shows ‘null’. So does it sucessfully insert into the database, or should I change another way to get the object from database.

Answer 1

collection.findOne is asynchronous, so you don’t use the return value of the function; instead, you should console.log(item) from inside your (currently empty) callback.

 db.collection('locations', function(err, collection) {
     var object= {word:'TEST'};
     collection.insert(object, {safe:true}, function(err, result) {
       collection.findOne({word:'TEST'}, function(err, item) {
          console.log(item);
       });
     });        
 });