nodejs mysql using data in other modules/files - mysql

Question

I'm trying to get data from my DB and use it in different modules of my app. My app is split in a lot of modules which I require where I need them.
My connectDB.js module looks like this
var mysql = require('mysql');
var db = mysql.createConnection({
host: "localhost",
user: "root",
password: "pw",
database : "something"
});
db.connect(function(err){
if(err){
console.log('Error connecting to Db');
return;
}
console.log('Database connected');
});
function select(query)
{
db.query(query,function(err,rows){
if(err) throw err;
return rows;
});
}
module.exports =
{
select
}
I was hoping to simply just require this module and then do a something like
db.select('SELECT * FROM users');
But for some reason the return value is always "undefined"
Sending queries inside the connectDB module works as expected returning the correct data. But I can't use my function to get data.
Is there something wrong here with my logic? Can you help what I am doing wrong?

Answer 1

As I remember, connection.query will return result async, so you need to wrap it with callback or Promise.
var mysql = require('mysql');
function DB {
var db = mysql.createConnection({
host: "localhost",
user: "root",
password: "pw",
database : "something"
});
db.connect(function(err){
if(err){
console.log('Error connecting to Db');
return;
}
console.log('Database connected');
});
this.select = function(query, callback) {
db.query(query,function(err,rows){
if(err) throw err;
callback(rows);
});
}
//Promise version
this.selectPromise = function(query) {
return new Promise(function(resolve, reject){
db.query(query,function(err,rows){
if(err) reject(err);
resolve(rows);
});
});
}
}
module.exports = DB;
How to use:
var DB = require('your-module');
var db = new DB();
db.query('select * from table', function(result) {
console.log(result);
});
db.selectPromise('select * from table').then(function(result) {
console.log(result);
});

Answer 2

Make the following change to your code
module.exports =
{
select: select
}
And you forgot about callback function
function select(query, callback)
{
db.query(query,function(err,rows){
if(err) throw err;
return callback(rows);
});
}
Then you can pass a function like this:
db.select('SELECT * FROM users', function(rows) {
// Do stuff with rows
});