MongoDB Connection Setup.

//database.js
const mongodb = require('mongodb');
const MongoClient = mongodb.MongoClient;
let _db;

const mongoConnect = (callback) => {
    MongoClient.connect(
    'mongodb+srv://RanaM:201505093@cluster0.bitxd.mongodb.net/<dbname>?retryWrites=true&w=majority'
    , { useUnifiedTopology: true,
        useNewUrlParser: true
    })
    .then( client => {
        console.log('Connected!');
        _db = client.db('test');
        callback(client);
    })
    .catch(err => {
        console.log(err);
        throw err;
    });
};

const getDb = () => {
    if(_db){
        return _db;
    }
    throw 'No Database found';
}

exports.mongoConnect = mongoConnect;
exports.getDb = getDb;


//app.js
const express = require('express');
const adminRoutes = require('./routes/admin');
const shopRoutes = require('./routes/shop');
const bodyParser = require('body-parser');
const path = require('path');
const app = express();
const errorController = require('./controllers/error');
const mongoConnect = require('./util/database').mongoConnect;

app.set('view engine', 'ejs');
app.set('views', 'views');

app.use(bodyParser.urlencoded({ extended: false}));

app.use(express.static(path.join(__dirname, 'public')));

app.use('/admin',adminRoutes);
//app.use(shopRoutes);

app.use(errorController.get404);

 mongoConnect((client) => {
    console.log(client);
    app.listen(3000);
});

//app.listen(3000);

///Sample Insert into Database.!

exports.postAddProduct = (req, res, next) => {
    const title = req.body.title;
    const imageUrl = req.body.imageUrl;
    const price = req.body.price;
    const description = req.body.description;
    const product = new Product(title,imageUrl,description,price);
    product
    .save()
    .then( result => {
      console.log('Added Product.!');
      res.redirect('/admin/products');
    })
    .catch(err => {
      console.log(err);
    });
};

///Using in Model
const getDb = require('../util/database').getDb;

class Product{
    constructor(title, price, description, imageUrl){
        this.title = title;
        this.price = price;
        this.description  = description;
        this.imageUrl = imageUrl;
    }
    save(){
        const db = getDb();
        return db.collection('products')
        .insertOne(this)
        .then(result => {
            console.log(result);
        }).
        catch(err => {
            console.log(err);
        });
    }

    static fetchAll(){
        const db = getDb();
        return db.collection('test')
        .find().toArray()
        .then(products => {
            console.log(products);
            return products;
        })
        .catch(err => {
            console.log(err);
        });
    }
}

module.exports = Product;