How do I create a MySQL connection pool while working with NodeJS and Express?

Question

I am able to create a MySQL connection like this:

var mysql      = require('mysql');
var connection = mysql.createConnection({
    host     : 'localhost',
    user     : 'me',
    password : 'secret',
    database : 'my_db'
});

connection.connect();

But I would rather like to initiate a pool and use it across my project.

Sadyesaechao

Answer 1

Just to help some one in future, this worked for me:

I created a mysql connector file containing the pool:

// Load module
var mysql = require('mysql');
// Initialize pool
var pool      =    mysql.createPool({
    connectionLimit : 10,
    host     : '127.0.0.1',
    user     : 'root',
    password : 'root',
    database : 'db_name',
    debug    :  false
});    
module.exports = pool;

Later you can simply include the connector in another file lets call it manageDB.js:

var pool = require('./mysqlConnector');

And made a callable method like this:

exports.executeQuery=function(query,callback){
    pool.getConnection(function(err,connection){
        if (err) {
          connection.release();
          throw err;
        }   
        connection.query(query,function(err,rows){
            connection.release();
            if(!err) {
                callback(null, {rows: rows});
            }           
        });
        connection.on('error', function(err) {      
              throw err;
              return;     
        });
    });
}

Sadyesaechao

hi.. so i am new to node too so i have some doubts. So the exports function will be in the connector file right?? and to call this, i will have to pass my query as a parameter? – Trefor

As an alternative to the pool.getConnection() -> connection.query() -> connection.release() code flow, you can now directly use the following flow - pool.query(query, (function(err,connection){... github.com/mysqljs/mysql#pooling-connections – Montemayor

Wouldn't that create a new pool connection every time I'll import mysqlConnector in a controller and not on my app.js? – Mimicry

Answer 2

You can create a connection file, Let's called dbcon.js

var mysql = require('mysql');

// connect to the db
dbConnectionInfo = {
  host: "localhost",
  port: "3306",
  user: "root",
  password: "root",
  connectionLimit: 5, //mysql connection pool length
  database: "db_name"
};

//For mysql single connection
/* var dbconnection = mysql.createConnection(
        dbConnectionInfo
); 

 dbconnection.connect(function (err) {
    if (!err) {
        console.log("Database is connected ... nn");
    } else {
        console.log("Error connecting database ... nn");
    }
}); 

*/

//create mysql connection pool
var dbconnection = mysql.createPool(
  dbConnectionInfo
);

// Attempt to catch disconnects 
dbconnection.on('connection', function (connection) {
  console.log('DB Connection established');

  connection.on('error', function (err) {
    console.error(new Date(), 'MySQL error', err.code);
  });
  connection.on('close', function (err) {
    console.error(new Date(), 'MySQL close', err);
  });

});


module.exports = dbconnection;

Now include this connection to another file

var dbconnection = require('../dbcon');
dbconnection.query(query, params, function (error, results, fields) {
    //Do your stuff
});

Clyde

When you are calling 'connect ' cmd or I don't need this? – Carolacarolan

If you want to check your db connection is established or not, then you can un-comment the connect cmd which is already mention in code, otherwise don't need to use. – Clyde

Answer 3

There is some bugs in Utkarsh Kaushik solution:

• if (err), the connection can not be released. connection.release();

• and when it has an err, next statement .query always execute although it gets an error and cause the app crashed.

• when the result is null although query success, we need to check if the result is null in this case.

This solution worked well in my case:

exports.getPosts=function(callback){
    pool.getConnection(function(err,connection){
        if (err) {
          callback(true);
          return;
        }
        connection.query(query,function(err,results){
            connection.release();
            if(!err) {
                callback(false, {rows: results});
            }
            // check null for results here
        });
        connection.on('error', function(err) {
              callback(true);
              return;
        });
    });
};

Narcosis

Answer 4

You do also can access the Mysql in a similar way by firstly importing the package by entering npm install mysql in the terminal and installing it & initialize it.

const {createPool} = require("mysql");

const pool = createPool({
    host     : 'localhost',
    user     : 'me',
    password : 'secret',
    database : 'my_db'
)};

module.exports = pool;

Bozuwa