How to reuse mongodb connection in node.js

Question

I'm using node-mongodb-native driver with mongodb to write a website.

I have a question about how to open mongodb connection once, then use it in collection name users in user.js and collection name posts in comment.js

I want to open db connection in db.js then to insert / save data for users and posts collection

Currently code,my db.js

var Db = require('mongodb').Db,
    Connection = require('mongodb').Connection,
    Server = require('mongodb').Server;
module.exports = new Db(
    'blog', 
    new Server('localhost', Connection.DEFAULT_PORT, {auto_reconnect: true})
);

I used db.js in user.js as follow

var mongodb = require('./db');

function User(user){
  this.name = user.name;
  this.password = user.password;
  this.email = user.email;
};

module.exports = User;

User.prototype.save = function(callback) {//save user information
  //document to save in db
  var user = {
      name: this.name,
      password: this.password,
      email: this.email
  };
  mongodb.close();
  //open mongodb database
  mongodb.open(function(err, db){
    if(err){
      return callback(err);
    }
    //read users collection
    db.collection('users', function(err, collection){
      if(err){
        mongodb.close();
        return callback(err);
      }
      //insert data into users collections
      collection.insert(user,{safe: true}, function(err, user){
        mongodb.close();
        callback(err, user);//success return inserted user information
      });
    });
  });
};

and comment.js

var mongodb = require('./db');

function Comment(name, day, title, comment) {
  this.name = name;
  this.day = day;
  this.title = title;
  this.comment = comment;
}

module.exports = Comment;

Comment.prototype.save = function(callback) {
  var name = this.name,
      day = this.day,
      title = this.title,
      comment = this.comment;
  mongodb.open(function (err, db) {
    if (err) {
      return callback(err);
    }
    db.collection('posts', function (err, collection) {
      if (err) {
        mongodb.close();
        return callback(err);
      }
      //depend on name time and title add comment
      collection.findAndModify({"name":name,"time.day":day,"title":title}
      , [ ['time',-1] ]
      , {$push:{"comments":comment}}
      , {new: true}
      , function (err,comment) {
          mongodb.close();
          callback(null);
      });   
    });
  });
};

Answer 1

You can connect once, and then reuse it as many times as you want:

var mongodb = require('mongodb');
var events = require('events');
var event = new events.EventEmitter();
var access = new mongodb.Server(host, port, { });
var client = null;

new mongodb.Db('YOUR DATABASE', access, { safe: true, auto_reconnect: true }).open(function (err, c) {
  if (!err) {
    client = c;
    console.log('database connected');
    event.emit('connect');
  } else {
    console.log('database connection error', err);
    event.emit('error');
  }
});

exports.get = function(fn) {
  if(client) {
    fn(client);
  } else {
    event.on('connect', function() {
      fn(client);
    });
  }
};

And then reuse it:

var db = require('./db');
var items;
db.get(function(client) {
  items = new mongodb.Collection(client, 'collection');
});

// then anywhere in your code
db.get(function() {
  // items.find({ ...
});