Develop Reference

How can I update the frontend after waiting for the database in the backend to update in Node.js/Express?

I saw a similar question posted Here, but they are using MEAN-Stack.
I am currently just using a 'setTimeout' function to wait a few seconds before requesting new data from the server using a fetch api to give it time to update but this doesnt feel like the right way to do it. Is there a simple way for the front-end to update only after the database is updated in Express? I am new to Node please forgive me.
app.js:
const express = require('express');
const app = express();
const mysql = require('mysql');
let viewData = {
//html data
}
var pool = mysql.createPool({
connectionLimit : 10,
host: "localhost",
port: 3306,
database: 'testing',
user: "root",
password: "pass"
});
function sql(type) {
if(type == 'select') {
//Select query here
}
if(request == 'addRow') {
//Insert query here
}
}
app.get(`/`, function (req, res) {
res.sendFile('./views/index.html', {root: __dirname});
})
app.post('/api/add', function(req, res){
res.setHeader('Content-Type', 'application/json');
sql('addRow')
});
app.get('/api/viewData', function (req, res) {
res.setHeader('Content-Type', 'application/json');
res.send(JSON.stringify(viewData));
})
index.js:
function loadData() {
fetch('/api/viewData')
.then(z => z.json())
.then(a => {
//update html
})
}
function postData(a) {
fetch('/api/add', {
method: 'POST',
headers: {
'Content-Type': 'application/json'
},
body: JSON.stringify({
//data to send to app.js
})
}).then(setTimeout(function(){loadData();}, 3000))
}

You should use async and await function
Example: After async/await
async function fun1(req, res){
let response = await request.get('http://localhost:3000');
if (response.err) { console.log('error');}
else { console.log('fetched response');
}
The complete code of our example is shown below:
npm install express jsonschema body-parser promise-mysql
var express = require('express');
var bodyParser = require('body-parser')
var app = express();
var validate = require('./validate')
var mysqlConnection = require('./connectionShare');
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());
const addItem = function(item, connection){
console.log("Adding Item");
return new Promise(function(resolve, reject){
connection.query("INSERT INTO product SET ?", item)
.then(function(result){
resolve(item.seller);
}).catch(function(error){
reject(error);
});
})
}
const findOrCreateUser = function(user,connection){
console.log("Finding User");
return new Promise(function(resolve,reject){
connection.query("SELECT * FROM user WHERE email=" + connection.escape(user.email))
.then(function(results){
if(results.length == 1){
resolve(results[0].id)
} else {
connection.query("INSERT INTO user SET ?", user)
.then(function(results){
resolve(results.insertId);
});
}
}).catch(function(error){
reject(error);
})
})
}
const selectUserItems = function(userID,connection){
console.log("Selecting Items " + userID);
return new Promise(function(resolve,reject){
connection.query("SELECT * FROM product WHERE seller = " + connection.escape(userID))
.then(function(results){
resolve(results);
}).catch(function(error){
reject(error);return;
});
})
}
app.post('/add/product', validate.JsonValidation, mysqlConnection.getConnection, async function(req,res){
var connection = req.connection;
var item = {
name: req.body.name,
price: req.body.price,
width: req.body.width,
height: req.body.height,
added: req.body.added,
image: req.body.image
};
var user = {
username: req.body.seller.username,
email: req.body.seller.email,
votes: req.body.seller.votes
};
try {
item.seller = await findOrCreateUser(user,connection);
var user_id = await addItem(item,connection);
var items = await selectUserItems(user_id, connection);
connection.connection.release();
res.status(200).json(result);
} catch(error) {
res.status(500).end(error);
}
});
process.on('uncaughtException', error => console.error('Uncaught exception: ', error));
process.on('unhandledRejection', error => {console.error('Unhandled rejection: ', error));
app.listen(8000, function () {
console.log('App listening on port 8000')
});

Cannot get any response from api created with Express.js and SQL Server

i'm trying to learn how to build an api with Node and Express.js. I've found the next step by step: click here
And created a very similar version but with my data:
var express = require("express");
var bodyParser = require("body-parser");
var sql = require("mssql");
var app = express();
app.use(bodyParser.json());
app.use(function (req, res, next) {
res.header("Access-Control-Allow-Origin", "*");
res.header("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, contentType,Content-Type, Accept, Authorization");
next();
});
var server = app.listen(process.env.PORT || 8080, function () {
var port = server.address().port;
console.log("App now running on port", port);
});
var dbConfig = {
user: "myUser",
password: "myPass",
server: "myServer",
database: "MyDB"
};
var executeQuery = function(res, query){
sql.connect(dbConfig, function (err) {
if (err) {
console.log("Error al conectarse a la base :- " + err);
res.send(err);
}
else {
// create Request object
var request = new sql.Request();
// query to the database
request.query(query, function (err, res) {
if (err) {
console.log("Error al correr query en la base :- " + err);
res.send(err);
}
else {
res.send(res);
}
});
}
});
}
//GET API
app.get("/api/ApiRequestData", function(req, res){
var query = "select * from [RequestData]";
executeQuery (res, query);
});
After create the server.js doc, executed with npm install and run with node server.js, i opened on postman using the next url: http://localhost:8080/api/ApiRequestData and get an error message: "Could not get any response". On the Node command prompt i get the message:
TypeError: res.send is not a function
at C:\Users\API\server.js:43:44
at C:\Users\API\node_modules\mssql\lib\main.js:1588:20
at Request.userCallback (C:\Users\API\node_modules\mssql\lib\tedious.js:853:61)
at Request.callback (C:\Users\API\node_modules\tedious\lib\request.js:33:27)
at Connection.message (C:\Users\API\node_modules\tedious\lib\connection.js:1179:27)
at Connection.dispatchEvent (C:\Users\API\node_modules\tedious\lib\connection.js:519:45)
at MessageIO. (C:\Users\API\node_modules\tedious\lib\connection.js:439:23)
at emitNone (events.js:106:13)
at MessageIO.emit (events.js:208:7)
at ReadablePacketStream. (C:\Users\API\node_modules\tedious\lib\message-io.js:92:15)
Someone knows why shows this message?
Hope you can help me.

You are shadowing res from line var executeQuery = function(res, query){... with res from line request.query(query, function (err, res) {.... Just rename the last res to something else and you won't get this error:
request.query(query, function (err, result) {
if (err) {
console.log("Error al correr query en la base :- " + err);
res.send(err);
}
else {
res.send(result);
}
});

You can use below query for fetching the records with hard coded query like.
I used same for my application.
sql.connect(config).then(() => {
return sql.query`select * from [dbo].[Customer]`
}).then(result => {
console.log(result)
}).catch(err => {
console.log(err);
})
Fetch the result using store procedure.
sql.connect(config).then(pool => {
return pool.request().input('Customerid', sql.Int, 2).execute("GetCustomerbyId")
}).then(result => {
console.log(result)
}).catch(err => {
console.log(err);
})

passing user input of html form to express node js without routing to a new page

I am trying to use imap to search emails in my gmail inbox. It is going to be server side mail parser. To do so, I used express and I want to receive the input of users (from search field) using express. However, all the solutions I searched in the internet use app.post and bring me to a new page. I don't want to show any thing new in user interface. I just want to receive the input of user and give it to a function which performs imap.search. Any help? Here is the code:
index.htm
<!doctype html>
<html>
<body>
<form action="http://127.0.0.1:8081/process_post" method="POST">
Search: <input type = "text" name = "Search_value"> <br>
<input type = "submit" value = "SEARCH">
</form>
</body>
</html>
test.js
var express = require('express')
var bodyParser = require('body-parser');
var app = express()
app.use(express.static('public'));
// use body parser to easy fetch post body
app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json())
var Imap = require('imap'),
inspect = require('util').inspect,
MailParser = require("mailparser").MailParser;
var imap = new Imap({
user: '***#gmail.com',
password: '*****',
host: 'imap.gmail.com',
port: 993,
tls: true
});
var fs = require('fs'), fileStream;
function openInbox(cb) {
imap.openBox('INBOX', true, cb);
}
// route to '/index.htm' to return the html file
app.get('/index.htm', function (req, res) {
res.sendfile('index.htm');
});
//route that receives the post body and returns your computation
app.post('/process_post', function (req, res) {
passtoserver(req.body, res);
});
app.listen(8081);
function passtoserver(parms, res) {
//get the parameters based on input name attribute from the html
//and parse strings to numbers
var m = parms.Search_value;
// res.writeHead(200, { 'Content-Type': 'text/html' });
res.end();
openInbox(function(err, box) {
if (err) throw err;
imap.search([ 'ALL', ['FROM', m] ], function(err, results) {
var f = imap.fetch(results, {
bodies: 'HEADER.FIELDS (FROM TO SUBJECT DATE)',
struct: true
});
f.on('message', function(msg, seqno) {
console.log('Message #%d', seqno);
var prefix = '(#' + seqno + ') ';
msg.on('body', function(stream, info) {
var buffer = '';
stream.on('data', function(chunk) {
buffer += chunk.toString('utf8');
});
stream.once('end', function() {
console.log(prefix + 'Parsed header: %s', inspect(Imap.parseHeader(buffer)));
});
});
msg.once('attributes', function(attrs) {
console.log(prefix + 'Attributes: %s', inspect(attrs, false, 8));
});
msg.once('end', function() {
console.log(prefix + 'Finished');
});
});
f.once('error', function(err) {
console.log('Fetch error: ' + err);
});
f.once('end', function() {
console.log('Done fetching all messages!');
});
});
});
}
imap.connect();
After submiting the user input, a new rout called process-post will ope. How to avoid this?

You can try it with:
https.request() API?
http.request() for secure protocal

child_process.fork - process.send does not return message

I am running this script with node child_process.fork api.
That is my express application script, from where I start my application:
/**
* Module dependencies.
*/
var express = require('express')
, routes = require('./routes')
, http = require('http')
, path = require('path');
var app = express();
//database connection
var connection = require('express-myconnection');
var mysql = require('mysql');
//all environments
app.set('port', process.env.PORT || 3000);
app.set('views', __dirname + '/views');
app.set('view engine', 'jade');
app.use(express.favicon());
app.use(express.logger('dev'));
app.use(express.bodyParser());
app.use(express.methodOverride());
app.use(express.static(path.join(__dirname, 'public')));
//development only
if ('development' == app.get('env')) {
app.use(express.errorHandler());
}
app.use(
connection(mysql,{
host: 'localhost',
user: 'root',
password : '',
port : 3306, //port mysql
database:'test-db'
},'pool')
);
//routes
//app.get('/', routes.index);
app.get('/', routes.list);
app.use(app.router);
//run script
var cp = require('child_process');
var child = cp.fork('dataGrabber/pusherMysql');
child.on('message', function(m) {
// Receive results from child process
console.log('received: ' + m);
});
http.createServer(app).listen(app.get('port'), function(){
console.log('Express server listening on port ' + app.get('port') + ' http://localhost:' + app.get('port'));
});
That`s the part where I run my script:
//run script
var cp = require('child_process');
var child = cp.fork('dataGrabber/pusherAPI');
child.on('message', function(m) {
// Receive results from child process
console.log('received: ' + m);
});
As you can see I load my script and want to receive a message from the child.
That is my pusherAPI.js script:
var mysql = require('mysql');
var Pusher = require('pusher-client');
/**
* connect with mysql db
*/
var connection = mysql.createConnection({
host : 'localhost',
user : 'root',
database : 'test-db',
port : '3306',
password : ''
});
connection.connect(function(err) {
if (err) {
console.error('error connecting: ' + err.stack);
return;
}
console.log('connected as id ' + connection.threadId);
});
//connect with the server
var API_KEY = 'cb65d0a7a72cd94adf1f';
var pusher = new Pusher(API_KEY, {
encrypted: true
});
var channel = pusher.subscribe("ticker.160");
channel.bind("message", function(data) {
console.log(data);
this.data = data;
/**
* save data to db
*/
var trade = {
timestamp : data.trade.timestamp,
price : data.trade.topbuy.price,
};
var query = connection.query('INSERT INTO trades SET ?', trade, function(err, result) {
if (err) {
connection.rollback(function() {
throw err;
});
}
//push message back to the app.js
process.on('message', function(m) {
// Pass results back to parent process
m = "insert happened";
process.send(m);
});
connection.commit(function(err) {
if (err) {
connection.rollback(function() {
throw err;
});
}
});
});
console.log(query.sql);
});
I want to send a message back to my app.js, whenever an insertion happened to my sql db
My script starts and runs my queries. However, process.send(m); does not send anything back.
Any recommendations what I am doing wrong?
I appreciate your answer!
Update
When changing my pusherAPI.js to, I get nothing back in the console.
var channel = pusher.subscribe("ticker.160");
process.on('insert_message', function(m) {
channel.bind("message", function(data) {
console.log(data);
this.data = data;
/**
* save data to db
*/
var trade = {
timestamp : data.trade.timestamp,
price : data.trade.topbuy.price,
};
var query = connection.query('INSERT INTO trades SET ?', trade, function(err, result) {
if (err) {
connection.rollback(function() {
throw err;
});
}
//push message back to the app.js
// Pass results back to parent process
m = "insert happened";
process.send(m);
connection.commit(function(err) {
if (err) {
connection.rollback(function() {
throw err;
});
}
});
});
console.log(query.sql);
});
});
In my app.js I changed my code like that:
//run script
var cp = require('child_process');
var child = cp.fork('dataGrabber/pusherAPI');
child.on('insert_message', function(m) {
// Receive results from child process
console.log('received: ' + m);
});

Move your process.send(m); outside of the message event handler. Otherwise you're adding a new message event handler for every query and those event handlers only fire when the parent process sends it a message. Example:
var channel = pusher.subscribe("ticker.160");
channel.bind("message", function(data) {
this.data = data;
/**
* save data to db
*/
var trade = {
timestamp : data.trade.timestamp,
price : data.trade.topbuy.price,
};
var query = connection.query('INSERT INTO trades SET ?',
trade,
function(err, result) {
if (err) {
connection.rollback(function() {
throw err;
});
return;
}
//push message back to the app.js
m = "insert happened";
process.send(m);
connection.commit(function(err) {
if (err) {
connection.rollback(function() {
throw err;
});
}
});
});
});

Asynchronous function not returning callback for MongoDB connect

I have a MongoDB connect call that crashes a heroku app..
I have been editing what was originally localHost code (was working perfectly) to work with Heroku MongoDb addons (like MongoLab), but how do I get someDBcollectionVariable to work with someDBcollectionVariable.find()
//MongoDB
var mongodb = require('mongodb');
var db;
var MONGODB_URI = process.env.MONGOLAB_URI;
var PORT = process.env.PORT;
var testColl;
function dbConnect() {
return mongodb.MongoClient.connect(MONGODB_URI, function(err, database) {
if(err) throw err;
db = database;
var testColl = db.collection('test');
app.listen(PORT);
console.log('Listening on port ' + PORT);
return testColl;
});
}
//calls then look like
app.post('/add', function (req, res) {
testColl.insert(
{
"title" : req.body.title,
"quantity" : parseInt(req.body.quantity)
},
function (err, doc) {
getAll(res);
});
});
//and getAll looks like this
function getAll(res) {
testColl.find().sort( { value: 1 } ).toArray(function (err, docs) {
res.json({docs: docs});
});
}
Before moving that code inside dbConnect(), testColl.find.. was generating a ResponseError because the connect code was completing before the variable could be set?

Returning a value from an asynchronous function makes no sense. To use the a value, you need to pass it to a callback function. The same goes for errors (you can't throw asynchronously). A fixed version of your code could look like:
//MongoDB
var mongodb = require('mongodb');
var db;
var MONGODB_URI = process.env.MONGOLAB_URI;
var PORT = process.env.PORT;
var testColl;
function dbConnect(callback) {
mongodb.MongoClient.connect(MONGODB_URI, function (err, database) {
if (err) {
return callback(err);
}
db = database;
database.collection('test', function (err, testColl) {
if (err) {
return callback(err);
}
app.listen(PORT);
console.log('Listening on port ' + PORT);
callback(null, testColl);
});
});
}
//calls then look like
dbConnect(function (err, testColl) {
if (err) {
return console.error(err.stack || err.message);
}
testColl.find...
});