node.js data fetch in json model error - json

Question

I am new to node.js
I was just making an simple application
my data is inserting properly into the database as well as fetching also from the database
But the problem is when I am trying to access it in json model it is giving me error
var express = require('express');
/*
* body-parser is a piece of express middleware that
* reads a form's input and stores it as a javascript
* object accessible through `req.body`
*
* 'body-parser' must be installed (via `npm install --save body-parser`)
* For more info see: https://github.com/expressjs/body-parser
*/
var bodyParser = require('body-parser');
// create our app
var app = express();
// instruct the app to use the `bodyParser()` middleware for all routes
app.use(bodyParser.urlencoded({ extended: true }));
// A browser's default method is 'GET', so this
// is the route that express uses when we visit
// our site initially.
app.get('/', function(req, res){
// The form's action is '/' and its method is 'POST',
// so the `app.post('/', ...` route will receive the
// result of our form
var html = '<form action="/" method="post">' +
'Enter your name:' +
'<input type="text" name="userName" placeholder="Put your name" />' +
'<br>' +'Enter your city:'+'<input type="text" name="userCity" placeholder="Put your city" />' +
'<br>' +'Enter your state:'+'<input type="text" name="userState" placeholder="Put your state" />' +
'<br>' +'Enter your country:'+'<input type="text" name="userCountry" placeholder="Put your country" />' +
'<br>' +
'<button type="submit">Submit</button>' +
'</form>';
res.send(html);
});
// This route receives the posted form.
// As explained above, usage of 'body-parser' means
// that `req.body` will be filled in with the form elements
app.post('/', function(req, res){
var userName = req.body.userName;
var userCity = req.body.userCity;
var userState = req.body.userState;
var userCountry = req.body.userCountry;
// var document = {userName:userName,userCity:userCity,userState:userState,userCountry:userCountry};
var html = 'Hello: ' + userName + '.<br>' +'City: ' + userCity + '.<br>'+'State: ' + userState + '.<br>'+'country: ' + userCountry + '.<br>'+
'Try again.';
// res.send(html);
//res.send(JSON.stringify(doc));
//lets require/import the mongodb native drivers.
var mongodb = require('mongodb');
var assert = require('assert');
var ObjectId = require('mongodb').ObjectID;
//We need to work with "MongoClient" interface in order to connect to a mongodb server.
var MongoClient = require('mongodb').MongoClient;
// Connection URL. This is where your mongodb server is running.
var url = 'mongodb://localhost:27017/test';
// Use connect method to connect to the Server
MongoClient.connect(url, function (err, db) {
if (err) {
console.log('Unable to connect to the mongoDB server. Error:', err);
} else {
//HURRAY!! We are connected. :)
console.log('Connection established to', url);
/* var userName = req.body.userName;
var userCity = req.body.userCity;
var userState = req.body.userState;
var userCountry = req.body.userCountry;
var document = {userName:userName, userCity:userCity,userState:userState,userCountry:userCountry};*/
// do some work here with the database.
var insertDocument = function(db, callback) {
db.collection('test').insertOne( {
"userName" :userName,
"userCity" : userCity,
"userState" : userState,
"userCountry" :userCountry ,
}, function(err, result) {
assert.equal(err, null);
console.log("Inserted a document into the test collection.");
callback(result);
});
};
var findDocument = function(db, callback) {
var cursor =db.collection('test').find( );
cursor.each(function(err, doc) {
assert.equal(err, null);
if (doc != null) {
console.log(doc);
// res.contentType('application/json');
res.send(JSON.stringify(doc));
/* app.get('/test', function(req, res, next) {
res.json(doc);
});*/
} else {
callback();
}
// res.send(JSON.stringify(doc));
});
};
MongoClient.connect(url, function(err, db) {
assert.equal(null, err);
insertDocument(db, function() {
findDocument(db, function() {
db.close();
});
});
});
/* var document = {name:"David", title:"About MongoDB"};
db.collection('test').insertOne(document, function(err, records) {
if (err) throw err;
console.log("Record added as "+records[0]._id);
});*/
//Close connection
// db.close();
}
});
});
app.listen(3000);
Please help me to get rid off the problem.
Thank you..
The error I am getting is cann't set headers after they are send

Answer 1

This kind of error usually means that you try using res.send(...) multiple times from the same route.
Here you can see that in your find document, you use a cursor.each, and send your result inside this cursor.each. This means that you send multiple results from the same route.
What you should do instead is having a variable that you use to store your result before sending it once everything is retrieved.