Playing with MongoDB - Finding documents

find.js

/////////////////////////////
// Playing with MongoDB ////
// 2 - Finding documents //
//////////////////////////

// MongoDB Driver instances.

var MongoClient = require('mongodb').MongoClient
,	ObjectId = require('mongodb').ObjectID

// Set the database and collection name you want to connect to perform the query.

,	database = "college"
, 	collection = "students";

// Since ObjectIds contain a timestamp, which tells you when the document was created,
// the next function converts a timestamp into an ObjectID. Allowing you to make queries
// by date without the necessity of inserting a timestamp key into your document schema 
// (unless you have persnickety requirements for creation times, like resolutions of less than a second, 
//	synchronization across app servers, etc). 

function objectIdFromTimestamp(timestamp) {

    // Convert string date to Date object (otherwise assume timestamp is a date).
    
    if (typeof(timestamp) == 'string') {
        timestamp = new Date(timestamp);
    }

    // Convert date object to hex seconds since Unix epoch.
    
    var	hexSeconds = Math.floor(timestamp/1000).toString(16)

    // Create an ObjectId with that hex timestamp.
    
    ,	constructedObjectId = ObjectId(hexSeconds + "0000000000000000");

    return constructedObjectId;
}

MongoClient.connect('mongodb://localhost:27017/' + database, function(err, db) {

	// A simple error handler.

	if (err) throw err;

	// Define the mongodb collection where your app will perform the query.

	var cursor = db.collection(collection)

	// Define the query parameters of the documents you are looking for.

	,	query = {
					_id: {
							$gt: objectIdFromTimestamp("2014/9/4"), 
							$lt: objectIdFromTimestamp("2014/9/6")
						},
					language: "EN"
				}

	// Define the filds you want to display after a succesful operation.

	,	projection = {
						_id: false, 
						student: false, 
						'personal_info.gender': false, 
						'personal_info.email': false, 
						career: false, 
						grades: false 
					};

	// MongoDB Find operation.
	// The operation will display only 10 documents
	// because of .limit(10)
	
	cursor.find(query, projection).limit(10).each(function(err, doc) {

		// It will display an error, if there is one.
		// Alse, it will display the returned documents
		// and close the database safely when the operation ends. 

		if (err) {
			throw err
		} else if (doc != null) {
			console.log(doc);				
		} else {
			db.close();
		}

	});

});