How to pass mongoDB object to all prototype functions in Javascript / JS.Node?

Question

I am using NodeJS together with MongoDB and have some issues with passing the mongoDB object to all my prototype functions. I don't understand how to pass this object between these prototypes. Maybe someone could point me in the right direction?

In my main file I create a new instance of my mongoDB object which contains all the prototypes I want to use to work with mongoDB. Then I use the prototype functions to connect and to create a new collection.

Main.js

var mongo = require('./database/mongoDB')
var mongoDB = new mongo();
// Connect to database
mongoDB.ConnectDB(dbPath);
// Create a collection
mongoDB.CreateNewCollection("Usernames");

The prototype functions are defined in MongoDB.js

MongoDB.js
// Get mongoDB

var mongoDB = require('mongodb').MongoClient;
var DatabaseOperations = function () {}; // Constructor

DatabaseOperations.prototype.ConnectDB = function(dbPath){
// Connect to database
mongoDB.connect(dbPath, function(err, mongoDatabase) {
if(!err) {
  console.log("Connected to database: " + dbPath);
  mongoDB.database = mongoDatabase;
} else {
  console.log("Could not connect to database, error returned: " + err);
}
});
}

DatabaseOperations.prototype.CreateNewCollection =   function(collectionName){
mongoDB.database.createCollection(collectionName, function(err,  collectionName){
if(!err) {
  console.log("Successfully setup collection: " + collectionName.Username);
  mongoDB.collectionName = collectionName;
} else {
  console.log("Could not setup collection, error returned: " + err);
}
});
}

I am able to connect to the database but from there on, I do not know how to pass the database object to other prototype functions in order to create a collection or do anything else with it. The error message I get when running it is this:

mongoDB.database.createCollection(collectionName, function(err, collection
TypeError: Cannot read property 'createCollection' of undefined

How do I get the database object into each of the prototype functions to work with it?

Answer 1

I see you found an alternative solution, but I'm going to comment anyway. Inside the constructor you should be doing something like

MongoDB.js
// Get mongoDB

var mongoDB = require('mongodb').MongoClient;
var DatabaseOperations = function () {}; // Constructor

DatabaseOperations.prototype.ConnectDB = function(dbPath){
// Connect to database
var that = this;
mongoDB.connect(dbPath, function(err, mongoDatabase) {
if(!err) {
  console.log("Connected to database: " + dbPath);
  that.database = mongoDatabase;
} else {
  console.log("Could not connect to database, error returned: " + err);
}
});
}

DatabaseOperations.prototype.CreateNewCollection =   function(collectionName){
this.database.createCollection(collectionName, function(err,  collectionName){
if(!err) {
  console.log("Successfully setup collection: " + collectionName.Username);
} else {
  console.log("Could not setup collection, error returned: " + err);
}
});
}

This way, you are assigning the database to the DatabaseOperations, and every prototype function of DatabaseOperations will have access to it through this.database. The database is now a property of the object. In general, different functions can only see stuff assigned to 'this' (DatabaseOperations).

Answer 2

I ended up using mongoskin as a driver for my Mongo database. By using mongoskin I was able to get a valid mongodb object to work with my collections in my prototype functions: http://www.hacksparrow.com/mongoskin-tutorial-with-examples.html