Keep getting Error: Can't set headers after they are sent

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.

Yi Kai Yi Kai · Accepted Answer · 2017-05-18T01:39:22

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();
            });

        });
    }
}

Keep getting Error: Can't set headers after they are sent

1 Answers