怎么用 mongoose 链接BAE的数据库

贴出部分代码

config.js

var config = {
 username:"4qakk7pmG5tkyl1mne6eS04n",
 password:"Oek6K2RpwPUoi0a2Obk0sAPDV0tBLUyi",
 db_host:"mongo.duapp.com",
 db_name:"zJIdwZIQgNwTSKddFmqM",
 db_port:"8908"
}

var localhost = {
 username:"",
 password:"",
 db_host:"localhost",
 db_name:"express-mongoose-demo",
 db_port:"27011"
}

module.exports = config;

db.js

var mongoose = require('mongoose');
var config = require('../config');

var db = exports.Db = mongoose.createConnection();
var options = {
    db: { native_parser: true },
    server: { poolSize: 5 },
    user: config.username,
    pass: config.password
}
db.open(config.db_host, config.db_name, config.db_port, options);

//监听BAE mongodb异常后关闭闲置连接
db.on('error', function (err) {
   db.close();
});

//监听db close event并重新连接
db.on('close', function () {
    db.open(config.db_host, config.db_name, config.db_port, options);
});

怎么调用