mysql function in nodejs working just for first time

I'm newbie in node.js I wrote a userModel module to do database stuff using MySQL and works fine but just for first time. When I refresh the page mysql data returns null

userModel.js // my module

var mysql = require('mysql');
var con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "",
  database: "database"
});

module.exports = {
    allUsers: function (callback) {
        con.connect(function (err1) {
            if (err1){
                return callback(err1, null);
            }
            con.query("SELECT * FROM users", function (err2, result, fields) {
                if (err2){
                    return callback(err2, null);
                }
                callback(err2, result);
            });
        });
    }
};

app.js // main js file

var express = require('express'),
    bodyParser = require('body-parser'),
    _ = require('underscore');

var app = express();
var port = process.env.PORT || 8080;
var User = require('./models/userModels');
var bookRouter = express.Router();


app.use(bodyParser.json());
app.use(bodyParser.urlencoded({extended:true}));


bookRouter.route('/books')

    .get(function (req, res) {

        User.allUsers(function (err, results) {

        var id = req.query.id;

        var somre = _.find(results , function (param) { //result is null in second refresh
            return param['id'] == id;
        });

        console.log(results);
        res.send(somre);
        });
    })

app.use('/api' , bookRouter)


app.get('/' , function (req , res) {
    res.send('welcome to my API');
});