Keep getting Error: Can't set headers after they are sent - node.js

Question

So I am trying out my code for updating and showing it to the user. Basically it is able to do what I need to do but after performing it I get this error
C:\Users\tester01_2\myproject\node_modules\mongodb-core\lib\cursor.js:174
throw err;
^
Error: Can't set headers after they are sent.
at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:357:11)
at ServerResponse.header (
C:\Users\tester01_2\myproject\node_modules\express\lib\response.js:725:10)
at ServerResponse.send
(C:\Users\tester01_2\myproject\node_modules\express\lib\response.js:170:12)
at C:\Users\tester01_2\myproject\dbUpdate.js:13:14
at C:\Users\tester01_2\myproject\dbUpdate.js:28:5
at handleCallback (C:\Users\tester01_2\myproject\node_modules\mongodb-
core\lib\cursor.js:171:5)
at nextFunction (C:\Users\tester01_2\myproject\node_modules\mongodb-
core\lib\cursor.js:682:5)
at Cursor.next [as _next]
(C:\Users\tester01_2\myproject\node_modules\mongodb-
core\lib\cursor.js:692:3)
at loop
(C:\Users\tester01_2\myproject\node_modules\mongodb\lib\cursor.js:694:8)
at _each
(C:\Users\tester01_2\myproject\node_modules\mongodb\lib\cursor.js:741:16)
This is my code
var MongoClient = require('mongodb').MongoClient;
var assert = require('assert');
var url = 'mongodb://localhost:27017/myproject';
module.exports = {
postCollection : function(req, res){
var issueQty = req.body.issueQty;
var itemDescrip = req.body.itemDescrip;
MongoClient.connect(url, function(err, db) {
assert.equal(null, err);
updateRecord(db, req, function(doc) {
return res.send('Record Found. Now updating this document...' +
itemDescrip + ' Record Updated. This is the new record ' + doc )
res.end();
db.close();
});
});
}
}
var updateRecord = function(db, req, callback) {
var cursor = db.collection('documents').find({'Item Description':
req.body.itemDescrip, 'Issued QTY': req.body.issueQty})
cursor.each(function(err,doc){
assert.equal(err, null);
if(doc != err){
console.log('Successfully queried');
console.log(doc);
callback(JSON.stringify(doc));
} else{
throw err;
}
});
db.collection('documents').updateMany(
{ 'Item Description': req.body.itemDescrip},
{
$set: { 'Issued QTY': req.body.issueQty }
},function(err, results) {
console.log(results);
console.log('Done');
console.log(results);
});
};
I think it has to do with my res due to all the threads I have seen being res being in a wrong position but I need to put my res.send there so that it can use doc. Is there any way to solve this problem? Thanks.

Answer 1

Firstly, you should remove return in front of res.send().
Secondly, in updateRecord function, the callback function shouldn't be called in a loop, it will execute multiple times. And you close the db before you execute updateMany.
If you want to send doc, you should use a temp array to hold the doc, and pass it to res when you finish all logics in updateRecord.
If I understand you correctly, following is my modification of your codes,
var MongoClient = require('mongodb').MongoClient;
var url = 'mongodb://localhost:27017/myproject';
var updateRecord = function(db, req, callback) {
db.collection('documents').updateMany({ 'Item Description': req.body.itemDescrip }, {
$set: { 'Issued QTY': req.body.issueQty }
}, function(err, results) {
if (err) return callback(err);
console.log('Done');
console.log(results);
var cursor = db.collection('documents').find({
'Item Description': req.body.itemDescrip,
'Issued QTY': req.body.issueQty
});
var temp = [];
cursor.each(function(err, doc) {
if (err) {
return callback(err);
}
console.log('Successfully queried');
console.log(doc);
temp.push(JSON.stringify(doc));
});
callback(null, temp);
});
};
module.exports = {
postCollection: function(req, res) {
var issueQty = req.body.issueQty;
var itemDescrip = req.body.itemDescrip;
MongoClient.connect(url, function(err, db) {
if(err) {
res.send(err);
res.end();
db.close();
return;
}
updateRecord(db, req, function(err, docs) {
if(err){
res.send(err);
}
else{
res.send(docs);
}
res.end();
db.close();
});
});
}
}