Requiring mongoose singleton after fetching from database - node.js

Question

I'm trying to build a singleton with mongoose to store my app config in the database, so instead of building a schema and model and exporting the latter with module.exports I'm fetching the config then exporting it, yet all I get is an empty JSON.
Here's my code for the config model:
var mongoose = require('mongoose');
var configSchema = new mongoose.Schema({
ad: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Ad'
},
max_users: Number
});
var configModel = mongoose.model('Config', configSchema);
configModel.findOne()
.populate('ad')
.exec((error, result) => {
if (!error) {
if (result) {
module.exports = result;
} else {
var default_config = new configModel({
ad: null,
max_users: 100
});
default_config.save();
module.exports = default_config;
}
} else {
throw error;
}
});
In the route, I'm only requiring the file and using it in a route
var config = require('../models/config');
router.get('/', function(req, res, next) {
res.json(config);
}
Please note that dynamically requiring the module in the route scope hasn't produced the problem.
Is it because require couldn't recognize exported variable in the asynchronous task ? Is there a proper way to handle this issue ?

Answer 1

require in CommonJS is synchronous. Try defining a file with no specific module.exports and requiring it in another file will give you a {}
The following might work.
var mongoose = require('mongoose');
var configSchema = new mongoose.Schema({
ad: {
type: mongoose.Schema.Types.ObjectId,
ref: 'Ad'
},
max_users: Number
});
var configModel = mongoose.model('Config', configSchema);
module.exports = function (cb) {
configModel.findOne()
.populate('ad')
.exec((error, result) => {
if (!error) {
if (result) {
module.exports = result;
} else {
var default_config = new configModel({
ad: null,
max_users: 100
});
default_config.save();
cb(null, default_config);
module.exports = default_config;
}
} else {
cb(error);
//throw error;
}
});
}
// In your routes
var config = require('../models/config');
router.get('/', function(req, res, next) {
config(function(err, val) {
if (err) {
// send back error
} else {
res.json(val);
}
})
}