how to do update operation in express.js - node.js

Question

I have a simple student database program in express.js using mongodb.How can the updation operation be performed for the following program:
my app.js programs is as follows:
var studentDb=new StudentDb('localhost',27017);
app.get('/',function(req,res){
studentDb.findAll(function(error,stu){
res.end(JSON.stringify({
title:'students',
students:stu
}));
});
});
app.get('/student/new',function(req,res)
{
var rollno=req.param('rollno');
studentDb.findByrollno(rollno,function(error,docs)
{
if( error ) { res.end(JSON.stringify(error)); }else{
if(docs.length==1)
{res.end('already has one.');}
else
{ studentDb.save({
title:req.param('title'),
name:req.param('name'),
rollno:req.param('rollno')
},
function(error,docs)
{
console.log(docs);
});setTimeout(function(){ res.redirect('/');},5000);}}
});
});
app.delete('/student/new', function (req, res) {
studentDb.findByrollno(req.param('rollno'), function (error, docs) {
studentDb.delete(req.param('rollno'),function (error,students) {
if (error) {
console.log(error);
} else {
console.log("deleted rollno: " + req.param('rollno'));
} res.end(JSON.stringify(students));
});
});
});
here is my studentdb.js file
var Db = require('mongodb').Db;
var Connection = require('mongodb').Connection;
var Server = require('mongodb').Server;
var JSON = require('mongodb').JSON;
var ObjectID = require('mongodb').ObjectID;
StudentDb = function(host, port) {
this.db= new Db('studentdata', new Server(host, port, {safe: false}, {auto_reconnect: true}, {}));
this.db.open(function(){});
};
StudentDb.prototype.getCollection= function(callback) {
this.db.collection('students', function(error, student_collection) {
if( error ) callback(error);
else callback(null, student_collection);
});
};
StudentDb.prototype.findAll = function(callback) {
this.getCollection(function(error, student_collection) {
if( error ) callback(error)
else {
student_collection.find().toArray(function(error, results) {
if( error ) callback(error)
else callback(null, results)
});
}
});
};
StudentDb.prototype.findByrollno = function(rollno,callback) {
this.getCollection(function(error, student_collection) {
if( error ) callback(error)
else {
student_collection.find({rollno:rollno}).toArray(function(error, results) {
if( error ) callback(error)
else callback(null, results)
});
}
});
};
StudentDb.prototype.save = function(students, callback) {
this.getCollection(function(error, student_collection) {
if( error ) callback(error)
else {
if( typeof(students.length)=="undefined")
students = [students];
for( var i =0;i< students.length;i++ ) {
student = students[i];
student.created_at = new Date();
}
student_collection.insert(students, function() {
callback(null, students);
});
}
});
};
StudentDb.prototype.delete = function(rollno,callback) {
this.getCollection(function(error, student_collection) {
if( error ) callback(error)
else {
student_collection.remove({rollno:rollno},function(error, results) {
if( error ) callback(error)
else callback(null, results)
});
}
});
};
i need to update a field in the student database.but i am unaware of using the update query.pls help me.

Answer 1

You mean you don't know how to implement a StudentDb.update method? You just need to make an object using Mongo's update operators. There are good docs on how to use these here. This method will update one student setting any fields you set in the updatedFields object in the student:
// updatedFields should be an object with fields to set on the student
// e.g. updatedFields = {name: "Bob", favouriteSubject: "Computing"}
StudentDb.prototype.update = function(rollno, updatedFields, callback) {
this.getCollection(function(error, student_collection) {
if( error ) callback(error)
else {
student_collection.updateOne(
{rollno: rollno},
{$set: updatedFields},
callback
);
}
});
};
Note that since your callbacks follow the callback(err, result) convention there's no need to call them yourself you can pass them to Mongo to call them for you.

Answer 2

From the MongoDb docs:
db.collection.update(
<query>,
<update>,
{
upsert: <boolean>,
multi: <boolean>,
writeConcern: <document>
}
)
Source: MongoD docs
You can create a new method on your StudentDb object prototype for handling update operations:
StudentDb.prototype.update = function (rollno, updatedFields, callback) {
this.getCollection(function(error, student_collection) {
if( error ) callback(error);
else {
student_collection.update({rollno: rollno}, updatedFields, function (err, updatedStudent) {
if (err) callback(err);
else callback(null, updatedStudent);
});
}
Add a new handler to your router using the PUT HTTP verb:
app.put('/student/new', function (req, res) {
studentDb.update(req.param('rollno'), req.body, function (err, student){
if (err) {
console.error(err);
} else {
res.send(JSON.stringify(student));
}
});
});
As a sidenote, you can check out the mongoose module for nodejs, working directly with the MongoDB native driver is a bit more verbose.
Also seeing that you are fairly new to nodejs, I suggest reading a bit more about RESTful services, the 'Content-Type' HTTP header and send your data in JSON format.
Improve your error handling when responding to HTTP requests (e.g. if the update operation fails, let the client know about it):
studentDb.update(req.param('rollno'), req.body, function (err, student){
if (err) {
console.error(err);
res.status(500).json(err); // respond with HTTP status 500 (internal server error)
} else {
console.log("updated rollno: " + req.param('rollno'));
} res.send(JSON.stringify(student));
});