Setting a function callback fram an async request - node.js

Question

Good Morning All,
I have been looking for an answer to this on the boards, but my noob brain just can't make sense of it.
i have this function in models/user.js
module.exports.getUserByUsername = function(username, callback){
var retUser = new User;
sql.connect(dbConfig, function(err) {
if (err) {
console.log(err);
callback();
}
// create Request object
var request = new sql.Request();
request.input('ip_username', sql.NVarChar, username)
// query to the database and get the records
request.query('select * from [portal_users] where username = #ip_username', function(err, recordset) {
if (err) {
console.log(err);
return;
} else {
var user = new User(recordset.recordset[0].username,recordset.recordset[0].password,recordset.recordset[0].email,recordset.recordset[0].name);
user.addID(recordset.recordset[0].id);
retUser = user;
}
callback();
// send records as a response
//res.send(recordset);
});
});
function callback() {
sql.close();
return retUser;
};
}
and this code in my routes/user.js
passport.use(new LocalStrategy(
function(username, password, done) {
User.getUserByUsername(username, function(err, user){
if(err) throw err;
if(!user){
return done(null, false, {message: 'Unknown User'});
}
User.comparePassword(password, user.password, function(err, isMatch){
if(err) throw err;
if(isMatch){
return done(null, user);
} else {
return done(null, false, {message: 'Invalid password'});
}
});
});
}));
I have been modifying an example from GITHUB that uses mongoDB for the DB connection, but I would like to use MS SQL. The function is successfully calling the database and returning the correct values. However I don't know how to initiate the callback so I can pass the retUser object back to the original function for processing and logging in.
I did for a moment try to do this by not using the callback and using a standard return type of function, however I quickly realised that given the async nature this wouldn't work.
any help here would be greatly appreciated.
Thanks

Answer 1

OK I managed to figure it out using this post:
Node.js npm mssql function returning undefined
my new code is:
module.exports.getUserByUsername = function(username, callback){
var connection = new sql.ConnectionPool(dbConfig, function(err) {
if (err) {
console.log(err);
callback(err);
return
}
// create Request object
var request = new sql.Request(connection);
request.input('ip_username', sql.NVarChar, username)
// query to the database and get the records
request.query('select * from [portal_users] where username = #ip_username', function(err, recordset) {
if (err) {
console.log(err);
callback(err,recordset);
return;
} else {
var user = new User(recordset.recordset[0].username,recordset.recordset[0].password.replace(/ /g,''),recordset.recordset[0].email,recordset.recordset[0].name);
user.addID(recordset.recordset[0].id);
callback(err,user);
}
sql.close();
// send records as a response
//res.send(recordset);
});
});
}