Playing with MongoDB - Updating documents

update.js

/////////////////////////////
/// Playing with MongoDB ///
// 3 - Updating documents /
//////////////////////////

// MongoDB Driver instance.

var MongoClient = require('mongodb').MongoClient

// Set the database and collection name you want to connect to perform the update.
 
,	database = "college"
, 	collection = "students";

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

	var cursor = db.collection(collection)
	,	temp = 0;

	cursor.find().each(function(err, doc) {
		
		if (err) {
			
			// A simple error handler.

			throw err;

		// Because of reading is faster than writing,
		// it's necessary to verify if there is any document to
		// update in order to prevent errors while updating.

		} else if (doc != null) {

			// Generate a final grade from the average grade
			// and a random value.

			var div = 4
			,	n1 = doc.grades.year1
			,	n2 = doc.grades.year2
			, 	n3 = doc.grades.year3
			, 	n4 = doc.grades.year4
			,	n5 = Math.round(Math.random()*100)
			,	average = (n1 + n2 + n3 + n4) / div
			,	year5 = (average + n5) / 2;
			
			// Update approved students.

			if (year5 > 55) {
				
				// Use the returned document as a criteria to find the document that is going to be updated.
				
				cursor.update(doc, {$set: {"grades.year5": year5, approved: true} }, function (err, updated) {
				
					// A simple error handler.

					if (err) throw err;
					
					// Count the number of updated documents in the database.
					
					temp += 1;
			

					// Since writing is slower than reading, it's necessary to close
					// the database after all files have been updated. So, when temp
					// reach 3000, which means the total documents in the collection, 
					// it will close the database safely.

					if (temp >= 3000) {
						db.close();
					}

				});

			// Update reproved students.

			} else {

				cursor.update(doc, {$set: {"grades.year5": year5, approved: false} }, function (err, updated) {
				
					// A simple error handler.

					if (err) throw err;

					// Count the number of updated documents in the database.
					
					temp += 1;
					
					// Close the database safely.

					if (temp >= 3000) {
						db.close();
					}

				});

			}
	
		}

	});

});