I've begun playing around with Node.js lately, for many reasons but most importantly the ease at which I can write a chat-server utilising HTML5 WebSockets. However, I've been stuck for weeks with MySQL.
I'm currently using this MySQL client module: https://github.com/sidorares/nodejs-mysql-native
I've connected to the database and managed to store data using the following code:
// MySQL database
var db = require("mysql-native").createTCPClient(); // localhost:3306 by default
db.auto_prepare = true;
db.auth(dbName, dbUser, dbPass);
// Update the database
db.execute("UPDATE server_data SET value='" + new Date() + "' WHERE name='lastLoaded'");
How may I go about retrieving data from the database using a SELECT * FROM x WHERE y=z query?
Is there any specific reason you chose nodejs-mysql-native over node-mysql which is a really good node module. If there is none, then you should probably try node-mysql. I've tried it and it is great to start off using MySQL with Node. You could do something like:
var mysql = require('mysql');
var connection = mysql.createConnection({
host : 'localhost',
user : 'your_username',
password : 'your_password',
});
connection.connect();
connection.query("UPDATE server_data SET value=? WHERE name=?", [new Date(), 'lastLoaded'] function(err, result) {
if (err) throw err;
console.log('Result: ', result);
});
connection.end();
The advantage you get by using it this way is that you can prevent SQL injection, which is taken care of internally in node-mysql (by using the connection.escape() method).
Related
I have used one signle connection object of MYSQL in node JS to serve for multiple users.
I mean to say that MySQL connection will be created upon starting the script & it will remain same until the life of the node script/server.
Practically, this is possible to do & i have done the same. Please take a look at below code of NodeJS/MySQL script.
#################################
var http = require('http');
var mysql = require('mysql');
var con = mysql.createConnection({
host: "192.168.1.105",
user: "root",
password: "XXXXXX",
database: "mydb"
});
con.connect(function(err) {
if (err) {
console.error('error: ' + err.message);
process.exit(1);
}
http.createServer(function (req, res) {
continueExecution(req,res);
}).listen(8082);
});
async function continueExecution(req,res){
res.write('calledddd\n');
for (let step = 0; step < 50; step++) {
// Runs 5 times, with values of step 0 through 4.
var bar = `Company Inc ${step}`;
var sql = `INSERT INTO customers (name, address) VALUES ('${bar}', 'Highway 37')`;
res.write(sql + "\n");
con.query(sql, function (err, result) {
if (err) throw err;
res.write("1 record inserted\n");
});
}
res.write('reached\n');
for (let ste = 0; ste < 50; ste++) {
res.write('started Update\n');
var bar = `Company Inc ${ste}`;
var sql = `UPDATE customers SET name = 'UPDATE RECORD' WHERE name = '${bar}'`;
con.query(sql, function (err, result) {
if (err) throw err;
res.write(result.affectedRows + " record(s) updated\n");
if(ste == 50) {
res.writeHead(200, {'Content-Type': 'text/html\n'});
res.write('Databse connected\n');
res.end();
}
});
}
}
#################################
I have several questions in my mind as i am technical expert. But i didn't find any resources over my questions. Please help me on this
Q1. Are there any type of consequences of using one single MySQL connection to provide response to multiple users?
Q2. Let's take an example.
100 users wants to access table name "users_data" at the same time. 25 users are updating their records on the same table with unique primary key. 50 users are selecting their records. another 25 users deleting their records.
All these operations are being done at the same time via parallel Node Script calls from remote device.
To complete all these MySQL transactions, system is using only 1 database connection.
What will happen in this case?
To answer your questions, one of the consequences of using a unique connection is that it can lead to slower request execution.
In fact, even if node will make the requests asynchronously, your database will execute all those requests synchronously, so one after the other in the order they came. As node makes the requests asynchronously, the order in which they are executed by your database is not granted, and the issue you are referencing to might happen.
One easy way to avoid this is to use a connection pool which will create a given number of connection, using the same db user. Here are some links that might help you with this :
using a connection pool with node.js
connect a mysql database with node.js
Currently I am experiencing a very frustrating issue with inserting data into my MySQL db using my NodeJS Express server.
My current setup is the following:
• MySQL server db on DigitalOcean droplet.
• NodeJS Express server on the same DigitalOcean droplet. It is being proxied by my Apache server that is on the same droplet. I keep Node server running with PM2.
I have been able to successfully read data from my db (i.e. SELECT * from performance);).
However, no matter what I try I cannot insert any data into my db. I have tried countless different solutions but none have worked.
Help would be greatly appreciated. Please ask any questions for further clarification if needed. Thank you.
My current code relating to MySQL:
server.js
var mysql = require('mysql');
var con = mysql.createConnection({
host: 'localhost',
user: 'user',
password: 'password',
database: 'analytics',
supportBigNumbers: true,
debug: true,
});
server.post('/performance', (req, res) => {
let d = req.body;
con.connect(function (err) {
if (err) throw err;
let q =
'INSERT INTO performance (uid, reqStart, resEnd, loadDuration) VALUES ?';
let values = []; // values to be inserted into db
// for testing purposes I have commented this out and tried inserting a hardcoded set of values instead
/*let body = JSON.parse(req.body); // json string body to json obj
body.data.forEach((x) => {
values.push([body.uid, x.reqStart, x.resEnd, x.loadDuration]);
});*/
values = [
[23299730, 8.3282343284, 8.121252244, 2.238932989],
[23288734, 8.3282343284, 8.121292244, 2.238932989],
];
con.query(q, [values], function (err, result) {
if (err) throw err;
});
});
res.send(d);
});
Update: I just ran my server manually (without PM2). This has allowed me to view console messages. For the first time I have seen a successful insert query. And upon running the server with PM2 I also get a successful query. However, on the second attempt I get PROTOCOL_ENQUEUE_HANDSHAKE_TWICE error.
Based on multiple other posts/articles I thought my code avoided this problem, but it's erroring on the line where I call con.connect(...). I have con.connect in a server.get route, but I haven't been hitting that endpoint at all.
After many hours of debugging, I think I found the problem.
Almost all tutorials showing how to connect to MySQL db using Node show that you should embed a con.query() call within a con.connect() call, and using connect() is recommended on MySQL docs.
However, con.query() also establishes a connection. Maybe it's because I am keeping the server live across multiple calls, but this results in the Handshake error I described in the post. Removing the wrapping con.connect() call fixed my problem.
I am trying to learn node.js so that I can actually get started on working on my personal project. I have been trying to follow the examples in the book "Learning node.js" (by Marc Wandschneider). I, at this point, decided to forgo practicing his example, and go straight into using his code as framework for my practice code.
In my practice code, all I am trying to do is connect to my RDS database (no, I am not using Elastic Beanstalk, btw), and output contents of one of the tables. Seems simple enough, but when I whip up the code for it (based on the book), it seems to attempt connection, but get hung up in the process. This is my code:
var pool = require('generic-pool');
var async = require('async');
var mysql = require('mysql');
var host = "<database-name>.cu8hvhstcity.us-west-2.rds.amazonaws.com",
database = "<database-name>",
user = "<username>",
password = "<someLongPassword>";
var dbClient;
async.waterfall([
// 1. establish connection to database
function (callback) {
console.log("Connecting to database " + database + "...");
dbClient = mysql.createConnection({
host: host,
database: database,
user: user,
password: password,
port: 3306
});
dbClient.connect();
},
// 2. select all from a table (let's go for locations)
function (cb)
{
var query = "SELECT * FROM locations"
console.log("running query \"" + query + "\"...");
dbClient.query(query, cb);
},
function (rows, fields, callback)
{
console.log(fields);
for (var i = 0; i < rows.length; i++)
{
console.log(JSON.stringify(rows, null, '\t'));
}
}
], function (err, results) {
if (err)
{
console.log("An error occurred...");
console.log(err);
}
else
{
console.log("Everything successfully completed!");
}
dbClient.end();
})
This is better than first attempt, when I put a database member to the argument passed to mysql.createConnection(), and it complained that database was unknown. In neither case did either "An error occurred..." nor "Everything successfully completed!" output to the window.
Is there any async stuff going on that is resulting in some kind of non-terminating infinite loop or something? How do I fix this?
The book has an associated GitHub page
NOTE:
Neither my example nor the cited GitHub code make use of that pool variable, so it can simply be commented out. All you need to do to run this yourself is to say npm install async,npm install mysql (as well as creating a dummy RDS database to point to, that contains locations table) before copying, pasting, and running this code.
EDIT:
I fixed the issue with database. I realized that the name of the database used '_', not '-'. Same issue (code hangs) still persists...
I did the following:
In the second function in the array, I needed two parameters, not one.
I fixed thus:function(results, cb)
The third function simply needed to callback(null)
I have a nodejs server in Openshift with a MySQL cartridge. It seems to build with no problem, however, when I try to query the database, it seems to be doing nothing... It doesn't even give me an error, it's just does nothing. Here's my relevant code.
var mysql = require('mysql');
var connection = mysql.createConnection({
host: 'mysql://' + process.env.OPENSHIFT_MYSQL_DB_HOST + ':' + process.env.OPENSHIFT_MYSQL_DB_PORT + '/',
user: process.env.OPENSHIFT_MYSQL_DB_USERNAME,
password: process.env.OPENSHIFT_MYSQL_DB_PASSWORD,
database: 'revision',
multipleStatements: true,
debug : true
});
And in the appropriate route:
var stuff = 'abc';
connection.query('SELECT 1', function(err, rows, fields){
if (err) {
stuff = "ghi";
} else {
stuff = "def";
}
});
stuff = stuff + "done";
res.send(JSON.stringify(stuff));
It should return "defdone" or "ghidone", but it always returns "abcdone"... It's like it doesn't even get inside the function. I've tried several ways of doing this and none work. I've dumped the connection variable and it seems to be what's meant to be.
The reason I'm using SELECT 1 as the query string was to verify it was not a database error.
It seems the "issue" had to do with the asynchronous nature of node, as the final 2 instructions are executed before the query is completed. Furthermore, the configs seemed to be wrong after all, as I only had a "host" attribute with the whole url. I changed it into to 2 attributes - "host and "port", giving them the appropriate variables (process.env.OPENSHIFT_MYSQL_DB_HOST and process.env.OPENSHIFT_MYSQL_DB_PORT). It's working now!
I'm just getting into coding server side javascript and have been reading tutorials on socket.io and node.js, but I haven't come across anything demonstrating how to use node.js to access a mysql database.
Say for instance I want to create a method that listens to a table in my database at
mysql.something.com (with database: database, username: username, etc), how would
I get socket.io with node.js to connect to that database and listen for new input to that table and then subsequently return that input?
I'm wondering if anyone could give me a specific example that uses a publish subscribe model.
Thanks for the help.
You have to poll mysql database for changes at regular interval and when detect a change emit a socket.io event. Here's a pseudo code
var mysql = require('mysql');
var connect = mysql.createConnection({
host: 'localhost'
, database: 'your_database'
, username: 'user'
, password: 'password'});
var initial_result;
// check for changes after 1 second
setTimeout(function(){
connect.query('select * from your_table', function(err, result) {
if(err) { throw new Error('Failed');}
initial_result = initial_result || result;
if(Changed(initial_result, result)) { socket.emit('changed', result); }
});
function Changed(pre, now) {
// return true if pre != now
}
}, 1000);