how to import function value from var require? - mysql

Question

I have this code:
server.js:
var sql = require('./libs/mysql');
app.get('/status', function(req, res) {
res.send(sql.readName('1600'));
});
mysql.js:
exports.readName = function(name){
var connection = mysql.createConnection(option);
connection.connect();
connection.query('SELECT id FROM asterisk.users WHERE name= '+name, function (err, rows, fields) {
console.log('mysql: ' +rows[0].id);
return(rows[0].id);
});
Now, when I send GET http://mydomain.com/status I can not receive responce. But in console log I see correct answer. Where is my error?

Answer 1

Most disk reading/DB access in node.js is done asynchronously. This allows node.js to be as fast as it claims. You need to use callback functions to handle the result of these read operations. If you are familiar with ajax, the concept is similar.
You are returning from connection.query which runs asynchronously. This is returned nowhere. readName actually returns nothing. What you need to do is actually pass in the callback that returns the value:
app.get("/status", function (req, res) {
sql.readName("1600", function (err, rows, fields) {
/* handle err */
res.send(rows[0].id);
});
});
This callback has to be called of course:
exports.readName = function (name, cb) {
/* snip */
connection.query(query + name, cb);
});

Answer 2

You can't get the result because the return statement is in the function function (err, rows, fields). You can use callback like this
var sql = require('./libs/mysql');
app.get('/status', function(req, res) {
sql.readName('1600', function(result){
res.send(result);
});
});
exports.readName = function(name, callback){
var connection = mysql.createConnection(option);
connection.connect();
connection.query('SELECT id FROM asterisk.users WHERE name= '+name,
function (err, rows, fields) {
console.log('mysql: ' +rows[0].id);
callback(rows[0].id);
});
}

Answer 3

Thanks for helping. I find http error causes described upper. Error appear if I use callback functions like this callback(row[0].id), but if we use syntax like this callback('id: '+row[0].id) everything it's ok. So when we send res.send(response) we cant send unnamed data, need to put there some descriptions.
So, my final code look like this:
server.js
var sql = require(./mysql);
app.get('/status', function(req, res) {
sql.readName('1600', function(result){
res.send(result);
});
});
mysql.js
var mysql=require(mysql);
exports.readName = function(name, callback){
var connection = mysql.createConnection(option);
connection.connect();
connection.query('SELECT id FROM asterisk.users WHERE name= '+name,
function (err, rows, fields) {
if(err) callback(err);
else{
console.log(rows[0].id);
callback('ID: '+rows[0].id);
}
});
return true;
};