Fetching data from a MySQL database using Promise

Question

I have written JavaScript code for fetching data from a MySQL database. I have used connection pooling and Promise API.

var mySql = require("mysql");
var Promise = require("promise");
var pool = mySql.createPool({
 host : "localhost",
 user : "root",
 password : "rahul",
 database : "testDb", //schema 
 connectionLimit : 13, // at a time 13 connection be created in pool
});
function getDepartments(){
 return new Promise(fn);
 function fn(resolve,reject){
 pool.getConnection(function(err,con){
 if(err){
 return reject(err);
 }else{
 con.query("select * from departmentTbl",function(err,rows){
 if(err){
 return reject(err);
 }else{
 con.release(); // releasing connection to pool
 return resolve(rows);
 }
 }); 
 }
 }); // getConnection
 }// fn
 } // getDepartments
getDepartments().then(function(rows){
 console.log(rows); 
}).catch(function(err){
 console.log(err); 
}).done(function(){
 pool.end(); // closing all connections in pool
});

Can I further improve the code? I have only used one Promise. Can I use multiple promises to avoid callback hell?

Answer 1

Resource leakage: put con.release() outside the else block.

• Stephen Rauch: Would you need to release on an error?
• mdfst13: @StephenRauch Yes, as per the documentation, you need to release on an error.