Mongodb: When do we need to expire shopping carts? - mongodb

Question

I'm building an e-commerce website by ExpressJs + Mongodb and I'm stuck with this concern:
When do we need to expire the cart ( remove the cart and return the product to inventory ) technically ? Whenever user visit the cart? or should I need a cron job?
I've followed this article: https://www.infoq.com/articles/data-model-mongodb
Here's my cart model's implementation:
'use strict';
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const CartItem = new Schema({
product: { type: Schema.Types.ObjectId, ref: 'Product' },
quantity: Number
});
const Cart = new Schema({
userSessionId: String,
status: {
type: String,
enum: [ 'active', 'completed', 'expiring', 'expired' ],
default: 'active'
},
items: [ CartItem ],
modifiedOn: { type: Date }
});
Cart.static({
summary: function(params, cb) {
this.aggregate([
{
$match: { userSessionId: params.userSessionId }
},
{
$unwind: {
path: '$items'
}
},
{
$lookup: {
from: 'products',
localField: 'items.product',
foreignField: '_id',
as: 'product'
}
},
{
$unwind: {
path: '$product',
preserveNullAndEmptyArrays: true
}
},
{
$group: {
_id: { userSessionId: '$userSessionId' },
count: { $sum: '$items.quantity' },
total: { $sum: { $multiply: [ '$product.price', '$items.quantity' ] } }
}
}
], (err, results) => cb(err, results[0]));
},
addProduct: function(params, cb, test) {
var d = new Date();
if (test) {
d.setMinutes(d.getMinutes() - 10);
}
this.findOneAndUpdate(
{ userSessionId: params.userSessionId },
{ $set: { modifiedOn: d } },
{ upsert: true, new: true }, (err, cart) => {
if (err) {
return cb(err);
}
const index = cart.items.findIndex((item) => {
return item.product.equals(params.productId);
});
if (index === -1) {
cart.items.push({
product: params.productId,
quantity: params.quantity
});
} else {
cart.items[index].quantity += parseFloat(params.quantity);
}
cart.save(cb);
});
},
updateQuantity: function(params, cb) {
this.findOneAndUpdate(
{ userSessionId: params.userSessionId },
{},
{ upsert: true, new: true }, (err, cart) => {
if (err) {
return cb(err);
}
const index = cart.items.findIndex((item) => {
return item.product.equals(params.productId);
});
if (index === -1) {
return cb(new Error('Can not find product in cart'));
}
cart.items[index].quantity = params.quantity;
cart.save(cb);
});
},
findItem: function(params, cb) {
this.findOne({ userSessionId: params.userSessionId }).exec((err, cart) => {
if (err) {
return cb(err);
}
const index = cart.items.findIndex((item) => {
return item.product.equals(params.productId);
});
if (index === -1) {
return cb(new Error('Can not find product in cart'));
}
cb(null, cart.items[index]);
});
},
removeProduct: function(params, cb) {
this.update(
{ userSessionId: params.userSessionId },
{
$pull: { items: { product: params.productId } },
$set: { modifiedOn: new Date() }
},
cb
);
},
getExpiredCarts: function(params, cb) {
var now = new Date();
if (typeof params.timeout !== 'number') {
return cb(new Error('timeout should be a number!'));
}
now.setMinutes(now.getMinutes() - params.timeout);
this.find(
{ modifiedOn: { $lte: now }, status: 'active' }
).exec(cb);
}
});
mongoose.model('Cart', Cart);

Answer 1

You should use some kind of distributed session to store the shopping cart!
I think you are looking for something like: https://www.youtube.com/watch?v=g32awc4HrLA
It uses expressjs-session and mongodb then you have a distributed cache and it will work with multiple instances of your application.