We Keep Coding

Res.redirect is not a function while using express in a nodejs webapp

I am trying to redirect to '/admin' route if the required data gets updated successfully but I am getting the error that res.redirect is not a function. I have tried writing return res.redirect also but it is also not working. Node experts, please help. Here I am just finding the student record on it's reg.no. basis and updating the record with its marks and redirecting to the admin page.
app.post('/admin/midterm/marks',(req,res)=>{
var m_written=[];
var m_practical=[];
var myjson=JSON.stringify(req.body);
course.subjects.map(sub=>{
if(!Array.isArray(req.body[`${sub}`]))
{
var p={subject:sub,mark:req.body[`${sub}`]}
m_written.push(p);
}
else{
var p={subject:sub,mark:req.body[`${sub}`][0]};
var q={subject:sub,mark:req.body[`${sub}`][1]};
m_written.push(p);
m_practical.push(q);
}
});
var first={
sem:course._id,
marks_sem:[{
term:ms,
m_written:m_written,
m_practical:m_practical
}]
}
if(!StudentRecord.total.length )
{
Student.updateOne({_id:check_Id},{total:first},function(err,res){
if(err)
{console.log("error");}
res.redirect('/admin');
});
}
else{
var flag=0;
StudentRecord.total.map(record=>{
if(record.sem==required_sem)
{
flag=1;
record.marks_sem.push(first.marks_sem);
Student.updateOne({_id:check_Id},{total:StudentRecord.total},function(err,res){
if(err)
{console.log("error");}
res.redirect('/admin');
});
}
});
if(flag==0)
{
StudentRecord.total.push(first);
Student.updateOne({_id:check_Id},{total:StudentRecord.total},function(err,res){
if(err)
{console.log("error");}
res.redirect('/admin');
});
}
}});

You override res in your callbacks. Name the second parameter in the callbacks result and everything will work fine.
app.post("/admin/midterm/marks", (req, res) => {
var m_written = [];
var m_practical = [];
var myjson = JSON.stringify(req.body);
course.subjects.map((sub) => {
if (!Array.isArray(req.body[`${sub}`])) {
var p = { subject: sub, mark: req.body[`${sub}`] };
m_written.push(p);
} else {
var p = { subject: sub, mark: req.body[`${sub}`][0] };
var q = { subject: sub, mark: req.body[`${sub}`][1] };
m_written.push(p);
m_practical.push(q);
}
});
var first = {
sem: course._id,
marks_sem: [
{
term: ms,
m_written: m_written,
m_practical: m_practical,
},
],
};
if (!StudentRecord.total.length) {
Student.updateOne({ _id: check_Id }, { total: first }, function (err, result) {
if (err) {
console.log("error");
}
res.redirect("/admin");
});
} else {
var flag = 0;
StudentRecord.total.map((record) => {
if (record.sem == required_sem) {
flag = 1;
record.marks_sem.push(first.marks_sem);
Student.updateOne(
{ _id: check_Id },
{ total: StudentRecord.total },
function (err, result) {
if (err) {
console.log("error");
}
res.redirect("/admin");
}
);
}
});
if (flag == 0) {
StudentRecord.total.push(first);
Student.updateOne(
{ _id: check_Id },
{ total: StudentRecord.total },
function (err, result) {
if (err) {
console.log("error");
}
res.redirect("/admin");
}
);
}
}
});

returning null when using value out of block

I am trying to query one collection, get IDs from that and with that I am querying another collection and send the response. No issue in that. My issue is I am using foreach, so I am trying to get the value out of block and send the response. But it's throwing null. I consoled the value inside the block, its giving the response but I couldn't access the value out of the block.
Code
getDetails = async (req, res) => {
let data: any[] = [];
await employee.find({
_id: new mongoose.Types.ObjectId(req.body.id)
}, (err, obj) => {
if (err) {
console.log("No Such Employee")
} else {
obj.forEach(element => {
employer.find({
user: new mongoose.Types.ObjectId(element.user)
}, (err, details) => {
if (err) {
console.log("No such employer")
} else {
for (var i = 0; i < detail.length; i++) {
let p_info = {
"id": detail._id,
"fname": details[i].fname "lname": details[i].lname "phone": details[i].phone,
"email": details[i].email,
}
data.push(p_info); // I can get value here
}
}
})
});
res.send(data); // Cannot get value here
}
});
}

return response only when all your asynchronous db calls are done. see below:
getDetails = async(req, res) => {
let data = [];
let employees;
try {
employees = await employee.find({
_id: new mongoose.Types.ObjectId(req.body.id)
});
} catch (err) {
console.log("No Such Employee");
}
let emp_len = employees.length;
employees.forEach((emp_obj, idx) => {
let details = await employer.find({
user: new mongoose.Types.ObjectId(emp_obj.user)
});
for (var i = 0; i < patient.length; i++) {
let p_info = {
"id": patient._id,
"fname": details[i].fname,
"lname": details[i].lname,
"phone": details[i].phone,
"email": details[i].email,
}
data.push(p_info); // I can get value here
}
if (emp_len == idx + 1) {
res.send(data); // Cannot get value here
}
});
}

Run loop on the server with node.js

Let's say i need to constantly collecting some data from a lot of clients and in parallel running some complex loop that solving some stuff with this data. How can i do it? Should i just write this in my piece of code:
app.get('/', function(req, res) {
res.sendFile(__dirname + '/public/views/index0.html');
});
io.sockets.on('connection', function(socket) {
// SOME STUFF WITH THE SOCKET
socket.on('disconnect', function(data) {
//SOME OTHER STUFF
});
});
while(...) {
//THE LOOP STUFF
}
Or i need to use the setTimeout() and setInterval() functions? How can i do the loop on the server that runs in parallel with the callbacks' stuff?

Don’t use while for make it, this block a thread. setTimeout() will run only once. You need to use setInterval() function.

You can use the async module to handle the async operation with the callback or use promise to avoid callback.
Here how I handle a complex async for each operation, that might helpfull to you get idea handeling ayncs forach
var cond = { _schedule: schedule_id }; // find curse by schedule id
Course.find(cond, function (err, courses) {
if (err) {
callback({ "success": false, "message": "Not able to update" });
} else {
async.forEachLimit(courses, 1, function (course, coursesCallback) {
async.waterfall([
function (callback) {
var schedule_date = moment(change_data.date).format('YYYY-MM-DD') + "T00:00:00.000Z"
var Assignmentcond = {
assignment_schedule_order: {
$gte: schedule_date
},
_course: course._id,
_schedule: schedule_id,
_user: userid
};
Assignment.find(Assignmentcond)
.populate({
path: '_course',
})
.lean()
.sort({ assignment_schedule_order: 1 })
.exec(function (err, AssignmentList) {
if (err) {
callback(null, '');
} else {
//console.log("------------------AssignmentList---------------------------");
//console.log(AssignmentList);
async.forEachLimit(AssignmentList, 1, function (ThisAssignmentCell, ThisAssignmentCellCallback) {
async.waterfall([
function (callback) {
var SearchObj = items;
var lebelObject = {};
for (var i = 0, flag = 0, insert = 0; i < SearchObj.length; i++) {
if (SearchObj[i].date == ThisAssignmentCell.assignment_schedule_date) {
flag = 1;
}
if (flag == 1 && SearchObj[i].label != "") {
if (ThisAssignmentCell.day == SearchObj[i].day_index) {
insert = 1;
var lebelObject = SearchObj[i];
break;
}
}
}
callback(null, ThisAssignmentCell, lebelObject, insert);
},
function (ThisAssignmentCell, SearchObj, insert, callback) {
console.log('----------------------');
console.log('ThisAssignmentCell', ThisAssignmentCell);
console.log('SearchObj', SearchObj);
console.log('----------------------');
if (insert > 0) {
var query = { _id: ThisAssignmentCell._id },
fields = {
assignment_date: moment(SearchObj.date).format('MM/DD/YYYY'),
assignment_schedule_date: moment(SearchObj.date).format('YYYY-MM-DD'),
assignment_schedule_order: new Date(SearchObj.date),
day: SearchObj.day_index,
dayNum: SearchObj.weekday_num
},
options = { upsert: false };
Assignment.update(query, fields, options, function (err, affected) {
callback(null, '');
});
} else {
// var cond = { _id: ThisAssignmentCell._id};
// Assignment.remove(cond)
// .exec(function (err, cnt) {
// callback(null, '');
// });
}
}
], function (err, result) {
// result now equals 'done'
console.log('done')
ThisAssignmentCellCallback();
});
}, function (err) {
console.log("Assignment For Loop Completed");
callback(null, AssignmentList);
});
}
});
}
], function (err, result) {
// result now equals 'done'
console.log('done')
coursesCallback();
});
}, function (err) {
console.log("courses For Loop Completed");
});
}
});

Node.JS Mongoose findOne With for Loop

How can i use the for loop with findOne from mongoose in node.js, maybe have other logic that i can do the same thing?
data = { _id: '598b4e9abe74280be0b0cb1b' }
{ _id: '598b4ec1be74280be0b0cb1c' }
{ _id: '598b4fa8be74280be0b0cb1d' }
{ _id: '5992feccdad6db0c603b260d' }
{ _id: '5995e4ce0b38ba123cf06654' };
notification = new Array();
for (var i = 0; i < data.length; i++) {
Message.findOne({ from: data[i]._id, to:socket.handshake.session.passport.user }, function(err, message){
if (err){
console.log('error');
}
if(!message.length){
console.log('no message!!');
}else{
notification.push(message);
}
});
}

If you can transform your input data into an array you can do this:
var data = [ObjectId('598b4e9abe74280be0b0cb1b'),
ObjectId('598b4ec1be74280be0b0cb1c'),
ObjectId('598b4fa8be74280be0b0cb1d'),
ObjectId('5992feccdad6db0c603b260d'),
ObjectId('5995e4ce0b38ba123cf06654')];
Message.find({from: {$in: data}, to:socket.handshake.session.passport.user})

Synchronize call in node.js

I am creating function in node.js from getting data from mongolab. It is just simple get method which return json
Here is my code:
app.get('/api/get_conversation_all_carer/:carer_id', function(req, res){
//Sender = user and receiver = carer
var values = [] ;
Conversation.aggregate([
{
$match: {
receiver_id: req.params.carer_id
}
},
{
$group: {
_id: "$sender_id",
}
}
],
function(err, result) {
if (err) {
console.log(err);
return;
}
for(var j = 0; j < result.length; j++) {
var object = {
"sender_id": result[j]._id,
"message": "",
"datetime": "",
"img": "",
"name":""
};
User.findOne({"_id": result[j]._id}, function(err, docs) {
object.img = docs.profile_pic;
object.name = docs.first_name;
});
Conversation.findOne({
$and: [
{
'receiver_id': req.body.carer_id
},
{
'sender_id': object.sender_id
}
]
},
{},
{
sort: {
'timer' : -1
}
},
function(err, docs) {
object.message = docs.message;
object.datetime = docs.timer;
values.push(object);
console.log("======= Inner =======");
}
);
}
console.log("====== OUT ======");
res = values;
}
);
});
Output:
====== OUT ======
====== Inner ======
I believe that Inner string should call first before Out, but here its happing reverse. I checked over other articals, but finding difficult to implement