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Close SQL connection Nodejs

I tried to close the connection for the below query by using connection.close(). but it is not working, so how to close connection inside route file
var express = require('express');
var router = express.Router();
var connection = require('../database.js');
var db = require('../database.js');
/* GET home page. */
router.get('/', function(req, res, next) {
connection.query("Select users..... ",function(err,supervisorrows) {
if(err){
req.flash('error', err);
res.render('View',{page_title:"Users - Node.js",supervisor:''});
}else{
res.render('View',{page_title:"Users - Node.js",supervisor:supervisorrows.recordset});
}
});
module.exports = router;

According to mysql npm docs There are two ways to end a connection :
connection.end() method
connection.destroy() method
The first one will make sure all previously enqueued queries are still before sending a COM_QUIT packet to the MySQL server.
The second one terminates a connection immediately and guarantees that no more events or callbacks will be triggered for the connection.

res.send() is not giving response on POST request in POSTMAN

hy, I'm learning nodeJS but when do post using postman data is saving in db but not displaying response in POSTMAN. On postman just displaying sending request... .
const express = require("express")
const app = express()
// dbConnection
require('./mongo')
// Models
require('./model/Post')
// MIDDLEWARE
app.use(express.urlencoded({extended: true}));
app.use(express.json())
const mongoose = require('mongoose')
const Post = mongoose.model("Post")
// POST REQUEST
app.post('/posts', async (req, res)=>{
// res.send(req.body)
try{
const post = new Post()
post.title = req.body.title
post.content = req.body.content
data = await post.save()
res.json(data)
}catch(error){
res.status(500)
}
})
app.listen(8000, ()=>{
console.log('Server is running on port:8000')
})

I don't think you're even running on a port, it says here
console.log('Server is running on port:8000')
})
All you do is console.log Server is running on Port 8000 with no back tick, therefore your not even running your server. This is why I think your Code is not working, test it out and see, if you get an error then you can debug from there. At least put some effort into debugging rather than immediately going on stack overflow. replace what you done with the port with this
// Create a variable called port and set it to your desired port
const port = 8000;
// Then hook it up to express.
console.log(`Server is running on port: ${port}`)
})
If the problem is still there then I think I have the solution to it
Check if you have mongoose and express installed
(it's npm i mongoose express)
I don't think you're even connected to your mongoose server, try doing this
const express = require("express")
const app = express()
// dbConnection
require('./mongo')
// Models
require('./model/Post')
// MIDDLEWARE
app.use(express.urlencoded({extended: true}));
app.use(express.json())
const mongoose = require('mongoose')
const Post = mongoose.model("Post")
// Hook it up to res
const port = 8000
// POST REQUEST
app.post('/posts', async (req, res)=>{
// res.send(req.body)
try{
const post = new Post()
post.title = req.body.title
post.content = req.body.content
data = await post.save()
res.json(data)
}catch(error){
res.status(500)
}
})
// Mongoose Connection
mongoose
.connect("your connection (it should be connection to application on mongo)", {
useNewUrlParser: true,
useUnifiedTopology: true,
useFindAndModify: true
})
.then(() => {
console.log("Connected to the database");
})
.catch((err) => {
console.log(err);
});
app.listen(8000, ()=>{
console.log(`Server is running on port: ${port}`)
})
Then once you've finished that, you established a connection to the mongodb server and should send the request to post

I think the catch block is executed. In this block, you only set the status of the response to 500 but you don't actually send the response to the client. That's why the Postman screen keeps blocking.
So, there are 2 things:
you need to send something to the client
you need to log the error to debug.
app.post('/posts', async (req, res)=>{
// res.send(req.body)
try{
const post = new Post()
post.title = req.body.title
post.content = req.body.content
data = await post.save()
res.json(data)
}catch(error){
console.log(error);// for debugging
res.status(500).send("ERROR_SERVER"); // send something to client
}
})

I have found the answer for your error, as I said in my old answer, running your tests would've worked, and showed you the error, however I have found the answer, I am assuming you have already found the solution (which is probably the same solution as mine) but if you haven't here's the problem.
The problem
It's very simple, you're creating a variable for mongoose after you required mongoose require('./mongo'); const mongoose = require('mongoose') This is wrong as JavaScript and most programming languages read code line by line (if not then all) so change this up to be instead the following:
Solution
const mongoose = require('mongoose');
require('./mongo');
Information
Create the variable before you require the package like so (in your code example):
const mongoose = require('mongoose');
require('./mongo');
If you have more problems
If you do have more problems then try to reinstall/update the package dependency for mongoose as following:
yarn add mongoose
or
npm install mongoose
If you do still have problems after the only think I can ask you to do is to change the line of code when it says
require('./mongo');
to either
require('./{filename}'); // Whatever the actual filename is.
or:
require('./mongoose');
Tips to improving your question
Even if my question doesn't work for your code make sure to paste the error message or the important parts of the error message into the question, otherwise this makes it hard to pinpoint what your error is. This makes it easier to find the solution for your code.

How to access application-level middleware from router?

I am trying to access my application-level middleware from router in a project generated with express application generator.
Middleware is used to query database with user ID received from router.
I feel like I'm missing something very simple (or fundamental) but can't get around the problem (this being my first Node.js project). So more than best practice I'm looking for a simple solution
I've tried using different app methods including post.
/app.js
var MyAppMidW = function (req, res, next) {
res.send(queryDB(req));
next()
}
app.use(MyAppMidW);
/routes/index.js
router.get("/dbquery", (req, res) => {
if (req.header('auth-header')) {
res.send(req.app.get.MyAppMidW(req.header('auth-header'))); //The problem
}
else {
res.send(req.app.get('defaultData')); //This works
}
});
Error messages include "$middleware is not a function" and "$middleware is not defined".
Solution
/app.js
app.MyAppMidW = function (req) {
queryDB(req);
}
/routes/index.js
router.get("/dbquery", (req, res) => {
if (req.header('auth-header')) {
req.app.MyAppMidW(req.header('auth-header'))); //Makes a database query
res.send(req.app.get('defaultData')); //Fetches database query result
}
else {
res.send(req.app.get('defaultData'));
}
});

If you do it like this
app.use(MyAppMidW);
Every request will query your db, and thats not what you want. I guess you use the MVC design pattern.
In your route folder you have something like this:
import appController from "../controllers/app.js"
router.get("/dbquery", appController.MyAppQuery)
And in your controllers folder you have your logic that querys the db
exports.MyAppQuery = (req, res){
//If u use mongodb for example
YourModel.find().then(data => {
res.json(data)
})
}

You need to call app.set("MyAppMidW", MyAppMidW) and then you can use get. Or do this inside the app.js file
app.MyAppMidW = function (req, res, next) {
res.send(queryDB(req));
next()
}
Then call it by req.app.get('MyAppMidW')(req.header('auth-header')) or req.app.MyAppMidW(req.header('auth-header')) inside the routes file.
But middleware is called automatically when you say app.use(MyAppMidW) the function is called by default on each request. So no need to call it explicitly inside the router function.

Hot reloading with express and chokidar causes a http headers sent error when using multiple routes

I've been trying a variety of setups for hot reloading and one that I've come across is the https://github.com/glenjamin/ultimate-hot-reloading-example/. Modifying this boilerplate code as a starting point, I've come across the following problem in my server code:
// server.js
import chokidar from 'chokidar';
import express from 'express';
const app = express();
// this is the middleware for handline all of my routes
app.use(function (req, res, next) {
require('./server/index')(req, res, next);
// if I commented out any additional routes, the setup would work fine
require('./server/foo')(req, res, next);
require('./server/catch-all')(req, res, next);
});
//this watches the server folder for changes
const watcher = chokidar.watch('./server');
watcher.on('ready', function () {
watcher.on('all', function () {
console.log("Clearing /server/ module cache from server");
Object.keys(require.cache).forEach(function (id) {
if (/[\/\\]server[\/\\]/.test(id)) delete require.cache[id];
});
});
});
app.listen(3000, 'localhost', function (err) {
if (err) throw err;
const addr = this.address();
console.log('Listening at http://%s:%d', addr.address, addr.port);
});
The above is the server code that handles clearing the cache by watching for changes with the chokidar module. If I have just one route required inside the app.use middleware function (which listens for every incoming request), I can get it to work. However if have multiple routes, the following error occurs:
Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client
This is a common issue posted on stack overflow, but all of the solutions I've come across and attempted haven't worked. My route files are as follows:
//index.js
import express from 'express';
const router = express.Router();
router.get('/', (req, res, next) => {
res.send("greagrehgarhegrehuh").end();
return next('router');
});
module.exports = router;
//end of index.js
//foo.js
import express from 'express';
const router = express.Router();
router.get('/foo', (req, res, next) => {
res.send("foo").end();
return next('router');
});
module.exports = router;
//end of foo.js
//catch-all.js
import express from 'express';
const router = express.Router();
router.get('*', (req, res, next) => {
res.send("catch all").end();
return next('router');
});
module.exports = router;
// end of catch-all.js
All three routes do the same thing, bar the endpoint. So far I've explicitly called end on each to end the response, used return next('router') to skip the rest of the middleware functions and have also tried doing it without the above as well. Any ideas on what I'm missing here to get this working? Here's a github project that showcases the issue
https://github.com/RonanQuigley/express-chokidar-hot-reload
UPDATE
So I actually removed the next calls and seem to have almost got it working by doing the following:
app.use(function (req, res, next) {
require('./server/index')(req, res, next);
require('./server/foo')(req, res, next);
});
// a second app.use middleware, that does the same
// as the catch all // * router.get from my original post
app.use(function (req, res, next) {
app.get('*', (req, res) => res.send('catch all'));
})
However, I can't use this second app.use with another require call to a file with an express router like the others. So it seems that express runs through the middleware stack, reaches the * and tries to set the header twice.
The reason I need the * is normally if a user requests an endpoint that doesn't exist, Node correctly shows up with cannot GET/. However, for some reason, with the setup I've outlined express will then crash. My workaround is using * at the end of the middleware stack and I'd just use a res.redirect to send the user back to wherever, but this causes the above issue I've outlined in my original post. So not sure how to get around that one.
So currently I have either:
1) Hot reloading works without the require for a router.get('*'), but when the user navigates to an endpoint that doesn't exist, express will crash.
2) Hot reloading works with the app.get('*') inside a second app.use call, but I can't then use a router to move this into a separate file.

Okay, so posting this solution up for my own future reference and in case somebody else stumbles into this problem.
After speaking with the express devs, it turns out that this is indeed possible with a combination of the following:
// you need to use comma separated routes
app.use(
dynamic('./server/index'),
dynamic('./server/foo')
);
// require the library at runtime and apply the req, res, next arguments
function dynamic(lib) {
return function (req, res, next) {
return require(lib).apply(this, arguments)
}
}
In the case of webpack, this would break it as you can't use require as an expression. So use the following to get around that:
function createRoutes(router) {
const dynamic = (lib) => {
return function (req, res, next) {
// let webpack generate a regex expression from this require
// if we don't you would get a critical dependency warning
// which would result in the routes not being found
return require("./src/" + lib + ".js").apply(this, arguments);
}
}
router.use(
dynamic('index'),
dynamic('foo'),
);
return router;
}

Let's step back a bit and talk about middleware.
Say you have a function which runs some kind of middleware.
const runMiddleware = (req, res, next) => {
console.log(`this will run everytime a HTTP request comes in`);
}
Then to use that middleware within express:
app.use(runMiddleware);
Every time any (GET, POST, DELETE, etc) request comes in, this function is run.
Essentially you are doing the same thing below - You are wrapping three (3) route calls with a single function. This function is calling all of these routes at once, hence res is actually being sent 3 times in a row in the example below:
app.use(function (req, res, next) { // runs every time any request comes in
require('./server/index')(req, res, next); // res sent, ok
require('./server/foo')(req, res, next); // res sent, err
require('./server/catch-all')(req, res, next); // res sent, err
});
Here is a basic way of handling routes:
const index = require('./server/index');
const foo = require('./server/foo');
app.use('/', index);
app.use('/foo', foo);
// catch everything else
app.use(function (req, res) {
res.send('catch all');
})

Node.Js webserver won't access data from mongodb

I just went through a tutorial and made a simple restful api. Afterwards, I added an admin user to my database. When I run the server, the authentication works, but if I try to access data via the api from the browser I get the eternal "waiting for response from localhost". I'm not sure what else I need to do for the request to be processed now that I've included a user authentication in mongodb.
var MongoClient = require('mongodb').MongoClient;
MongoClient.connect("mongodb://admin:password#localhost/bookstore?authSource=admin");
app.get("/", function(req, res){
res.send("Hello World");
});
When going to localhost:3000/ I see hello world, but localhost:3000/api/books won't return anything
app.get("/api/books", function(req, res){
Genre.getBooks(function(err, books){
if(err){
throw err;
}
res.json(books);
});
});
Here's the getBooks function
module.exports.getBooks = function(callback, limit){
Book.find(callback).limit(limit);
};

You're not in any way handling the callbacks from Node correctly. You also haven't defined what Genre or Book is in your answer.
That said, a couple notes. First, if you are in a callback, you never want to throw an error (as in don't use the syntax throw err), instead you want to either handle it or pass it back to your calling code.
A common approach I use would be like this:
app.get("/api/books", function(req, res, next){ // note adding next here
Genre.getBooks(function(err, books){
if(err){
return next(err);
}
return res.json(books);
});
});
// sometime later, a generic error middleware. You can make yours more useful
app.use((err, req, res, next) => {
return res.status(500).send({ message: 'An error has occurred' });
});
Your mongoclient connection and getBooks syntax are also probably wrong, but I can't advise you the best way to fix it without knowing if you're using Mongoose or if you're doing something else.
Ok, so since you're using Mongoose, you should remove the MongoClient code you have. Instead, add at app startup:
const mongoose = require('mongoose');
mongoose.connect('your connectionstring here');
and your getBooks should look like this:
module.exports.getBooks = function(callback, limit){
Book.find({}).limit(limit).exec(callback);
};
As a sidenote, node apps typically use the callback as the final argument in a parameter list, so you might want to change the function signature to (limit, callback) and adjust the calling code accordingly.

I figured out the problem. I didn't have mongoose properly set as the client, so when referencing the exported code for finding the book data nothing happened.