System Design - lesson 3 | HackIndia Skills

System Design - lesson 3 | HackIndia Skills | HackIndia

Example

Design note example

Add a short note like this in your README or system design section. Keep it specific to your project.

Database choice

We use PostgreSQL for this food pre-order app.

Main data:
- users
- canteens
- menu_items
- orders
- order_items
- payments

Why SQL:
- Orders have clear relationships with users, menu items, and payments.
- We need transactions so an order and its order items are saved together.
- We need queries like: show all orders for one user, show pending orders for one canteen, and calculate daily sales.

Trade-off:
- Schema changes take more planning than MongoDB.
- In return, we get safer relationships and easier reporting queries.

Tip

Use AI carefully

You can ask an AI tool to compare SQL and NoSQL for your app. Give it your screens, data, and queries. Do not accept a generic answer.

Check if it mentions your actual read and write patterns. If it only says “NoSQL is scalable” or “SQL is structured,” ask it to rewrite using your project details.

Prompt:
I am building a hackathon app for college mess pre-ordering.
Screens: menu list, cart, order status, admin order dashboard.
Data: users, menu items, orders, order items, payments.
Main queries: show menu by canteen, create order with items, show pending orders for admin.
Should I use PostgreSQL or MongoDB? Give a short design note with 2 trade-offs.

Choose SQL or NoSQL

Pick for access

When SQL fits

When NoSQL fits

Decision steps

Avoid vague reasons

Design note example

Use AI carefully

Do this now

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