NodeJS / Express 4 - Sqlite3 - Storing rowset into variable - node.js

Question

I'm trying to store the rowset from the query below into a variable so I can play it into the view and loop through it.
I'm getting results from the DB, and can console.log them in the db.each block, and I thought I could generate my JSON object below and then store it - but it's not setting it for some reason and var data = "" just returns an empty string.
I am a bit baffled as to why - does anyone know where I am going wrong please?
Thank you for taking the time to read.
var express = require('express');
var router = express.Router();
var db = require('../lib/db.js');
/* GET contacts listing. */
router.get('/', function(req, res) {
var data = "";
db.serialize(function() {
var rowset = db.each("SELECT b.forename, b.surname FROM contacts a, contact_attributes b WHERE a.contact_id = b.contact_id", function(err, row) {
data = ' { "'+row.contact_id+'" : [ { "forename" : "'+row.forename+'", "surname" : "'+row.surname+'" } ] } ';
});
});
res.render('contacts', {
title: "Contacts",
active: "contacts",
contacts: JSON.stringify(data)
});
});
module.exports = router;

Answer 1

The database query runs asynchronously, executing the callback function once the query returns. Therefore, res.render is called after data gets set to empty string, but before it gets set to the result set.
Also, there is no need to JSON.stringify a string that you have already built as JSON.
The code executes as follows:
var data = "";
db.serialize
var rowset = db.each
res.render
DB query returns.
db.each callback function executes, which sets data based on the result set.
Try this:
db.serialize(function() {
var rowset = db.each("SELECT forename, surname FROM contacts a, contact_attributes b WHERE a.contact_id = b.contact_id", function(err, row) {
var data = ' { "'+row.contact_id+'" : [ { "forename" : "'+row.forename+'", "surname" : "'+row.surname+'" } ] } ';
res.render('contacts', {
title: "Contacts",
active: "contacts",
contacts: data
});
});
});
});
or, avoid the manual JSON stringification:
db.serialize(function() {
var rowset = db.each("SELECT forename, surname FROM contacts a, contact_attributes b WHERE a.contact_id = b.contact_id", function(err, row) {
var data = {};
data[row.contact_id] = [
{
forename: row.forname,
surname: row.surname
}
];
res.render('contacts', {
title: "Contacts",
active: "contacts",
contacts: data
});
});
});
});