Inventory: Task 1 : Online Store

Task 1 : Online Store

### Q1: Describe what you think happened that caused those bad reviews during our 12.12 event and why it happened.

Answer :

1. You got a race condition on the checkout and payment flow.
2. Maybe, No stock check before user do a payment.
3. Not using DB transaction, so anything db action fail in a flow, data are not rolling back.
4. Qty should not have a negative value, although some business allow this behaviour.

( On my previous company, we can have negative stock so customer still can do a payment and company not loosing some sales. Company can order it and said to customer will delivery it 2-3 days again )

### Q2. Based on your analysis, propose a solution that will prevent the incidents from occurring again.

Answer :

It is a quite challenging problem, and should be a business problem not a software problem.

https://softwareengineering.stackexchange.com/questions/412515/should-an-e-commerce-application-reserve-products-before-attempting-payment

On Software Engineer POV, we can do things like:

1. Add a reserved system on an item
2. Auto change transaction for the losing customer to pre-order ( of course with terms updated/stated in the company t&c )
3. Check all code, for race condition with go race detector and fix that

go run --race race.go

Option 1 : Add a reserve system on an item

  Condition
  - Item A with stock qty is => 1 pc
  - User 1, 2, 3 add to chart in the same time 0.1-1ms ahead of each

The business flow and/or terms of use should mention :

• The stock will not be guaranteed to you until you pay

User 1 POV

• When user 1 add an item to cart, deduct the quantity of that item, and had a new table for reserved_item and set expired time for payment
• If user 1 checkout, do the payment, the item will belongs to user 1 => item A will be 0
• If user 1 not continue the checkout and not doing any payment, after the expired time is passing, the item will back available.

User 2 POV

• user 2 will not success add item to cart

User 3 POV

• user 3 will not success add item to cart

Pro :

• Stock quantity will be match and no race condition

Cons :

• If the expired time is too long and user 1 abandoned the cart, we may lose sales from user 2.
• Business will lose sales, because item can't be back ordered.

Run the Demo

On this demo we use the option 1, with scheduler set to 10s ( to reset reserved item )

you can run local using this step or go to public demo on :

http://fiberpos.primeracloud.com

or click here

Database

we are using mariadb, database migration and seed for initial data on app run

start db using local docker

docker-compose up -d

db will be accessible on localhost:3366 with user:pass dev:dev

Authentication

All route protected by JWT, except auth

login first using this credential to get token on {{url}}/api/v1/auth

email : [email protected]
pass : password123

Run on localhost

• clone this repo or run : go get github.com/randhipp/inventory
• copy .example.env to .env

❯ go run main.go
Connection Opened to Database
Database Migrated & Data Seeded

 ┌───────────────────────────────────────────────────┐ 
 │                   Fiber v2.22.0                   │ 
 │               http://127.0.0.1:3000               │ 
 │       (bound on host 0.0.0.0 and port 3000)       │ 
 │                                                   │ 
 │ Handlers ............ 25  Processes ........... 1 │ 
 │ Prefork ....... Disabled  PID ............. 18968 │ 
 └───────────────────────────────────────────────────┘ 

Documentation

All API route documented on POSTMAN with example respond ( success & err ) Download Postman Collection Here