NodeJS procedure execution flow - node.js

Question

I am new to Nodejs and aslo coming from a procedural language background so I have this need to know the execution flow of my code. I have a general question about the flow of Nodejs procedures. This is the scenario:
The code structure:
Appnamefolder
...standard node folders(.idea,css,fonts,etc)
...model
....database.js (connect to db and execute db queries)
...public
...routes
....users.js (GET and POST procedures....calls db queries via module.export)
...views
...app.js
...other js files
The question concerns the database. Since the DB connect is not in the app.js file but in a .js file in the model folder at what point is the DB connection made? and is a connection made every time a DB query is made?
What I hope to happen is that the DB connect is made one time and remain connected until the app is terminated. I tried putting the DB connect in app.js but I get an error when I attempt a DB query so I have to place the DB connect in the same file as the DB queries......Somehow this seems wrong to me. Can anyone explain how node handle this flow?....will be appreciative of any assistance.
EDIT: HERE IS A SAMPLE OF THE CODE
app.js
var express = require('express');
var path=require('path');
var bodyParser = require('body-parser');
var cookieParser=require('cookie-parser');
var expressSession=require('express-session');
var expejs = require('ejs');
var expressValidator = require('express-validator');
var flash = require('connect-flash');
var expressSession = require('express-session');
var expressLayouts=require("express-ejs-layouts") // add this requirement
var passport = require('passport');
var LocalStrategy = require('passport-local').Strategy;
var crypto = require("crypto");
var loaddealerTable=require('./loaddealerTable');
//var neo4j = require('neo4j-driver').v1;
// var neo4jdb = neo4j.driver("bolt://localhost:7474", neo4j.auth.basic("neo4j", "password"),
// {
// trust: "TRUST_ON_FIRST_USE",
// encrypted:true
// });
//***************Notifications Permission*******
var routes = require('./routes/index');
var users = require('./routes/users');
var csocket=require('./socketconnections');
var app=express();
var server=require('http').createServer(app);
sockets = require('./socketserver');
//rpaMessageWaiting = require('./getRPAmessages');
//var io=require('socket.io').listen(server);
// View Engine
app.set('views', path.join(__dirname,'views'));
app.set('view options', { layout:'layout.ejs' });
app.set('view engine','ejs');
//bodyParsers middleware
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
app.use(cookieParser());
app.use(expressLayouts);
//set up public folder
app.use(express.static(path.join(__dirname, '/public')));
// set express session with secret
app.use(expressSession({ secret: process.env.SESSION_SECRET || 'secret',
resave: true,
saveUninitialized: true
}));
// Passport initialization
app.use(passport.initialize());
app.use(passport.session());
//Express Validitor...validate inputs..taken from github middleware options
app.use(expressValidator({
errorFormatter: function(param, msg, value) {
var namespace = param.split('.')
, root = namespace.shift()
, formParam = root;
while(namespace.length) {
formParam += '[' + namespace.shift() + ']';
}
return {
param : formParam,
msg : msg,
value : value
};
}
}));
// connect flash middleware
app.use(flash());
// set global variables for flash messages
app.use(function (req, res, next)
{
res.locals.success_msg = req.flash('success_msg');
res.locals.error_msg = req.flash('error_msg');
res.locals.error = req.flash('error');
res.locals.user = req.user || null;
next();
});
// Middelware for route files
app.use('/', routes);
app.use('/users', users); //need to check routing
sockets.startSocketServer(server);
//load dealer table
console.log("load dealer table");
**loaddealerTable(); //First call on the DB**
//============socket io listening=======================
app.set('port',(process.env.PORT|| 3000));
server.listen(app.get('port'), function()
{
console.log('Server started on port '+app.get('port'));
// console.log('Server started on port .....');
// app.get('/index',function (req,res) {
// // body...
// res.render(__dirname+'/index');
});
loaddealertable.js
var loaddealerTable=function()
{
var memorytbl=require('./memorytables');
var User = require('./model/user');
var getHashKey=require('./gethashkey');
const hashMax=1000;
console.log("call get dealers from DB");
User.getallDealers(function(err,dealerFound,result)
{
if (dealerFound)
{
//
for (i=0; i< result.records.length; i++)
{
memorytbl.Dealer.email =result.records[i].get(0).properties.email;
memorytbl.Dealer.name =result.records[i].get(0).properties.name;
memorytbl.Dealer.telephone =result.records[i].get(0).properties.storenumber;
memorytbl.Dealer.creditcard =result.records[i].get(0).properties.creditcard;
memorytbl.Dealer.delivery =result.records[i].get(0).properties.delivery;
memorytbl.Dealer.location =result.records[i].get(0).properties.location;
memorytbl.Dealer.rating =result.records[i].get(0).properties.rating;
var hashIndex = getHashKey(memorytbl.Dealer.email ,hashMax);
memorytbl.DealersQ[hashIndex]=memorytbl.Dealer;
} //end of for i
} //end of if....
else
{
console.log("No dealers found....table is empty");
}
}) //end of loaddealers table db call
} //end of load dealers table function
module.exports=loaddealerTable;
user.js
var express = require('express');
var bcrypt = require('bcryptjs');
var router = express.Router();
var neo4j = require('neo4j-driver').v1;
var driver = neo4j.driver("bolt://localhost", neo4j.auth.basic("neo4j", "password"));
var session = driver.session();
//============Load Memory Tables=========================
router.getallDealers=function(callback) {
session
.run ("MATCH (user:Dealer) RETURN user")
.then (function(result)
{
if ( !result.records[0])
{
console.log("No Dealers Found");
session.close();
if (typeof callback==="function") {
return callback(null,false,result);
}
} // end of if not found
else
{
console.log("Dealer Found");
session.close();
if (typeof callback === "function")
{
return callback(null, true, result);
}
}
// or close session here??
}) //end of .then block
.catch(function(err)
{
console.log("DB call error: "+err);
}); //.then block
} //end of get dealers

Answer 1

For a start you have to understand that each file is a module.
Your app starts with running a single js file (module) like node app.js.
One module can load another module and another and so on.
Your folder structure does not have any effect on the order by itself. It all depends on your code and in what order do you load modules. While your sync code will run in the order you write it your async code will run in the future and you need to understand the event loop to understand what happens in your code.
From the small context you gave I guess you might tried to query your database before you connected to it. I don't see your code but it can happen regardless of where you connect (app.js file or another).