volfpeter / coupon-app

Example application using FastAPI + sqlmodel

Coupon management example application

Notes

A company offers various paid services to its customers and occasionally they want to issue coupons. This is a super-simple coupon management application that solves this using FastAPI and an SQL backend.

There are (at least) two types of coupons:

• fixed sum,
• percentage-based.

Q: Does fixed sum coupons need a currency? A: Probably not, we can convert on the UI if needed, although in that case we could end up with ugly, fractional numbers.

The application should provide a REST API for:

• creating coupons,
• checking coupon validity,
• activting/using coupon,
• disabling coupons.

A coupon could belong to a single customer, or it can be used by anyone who has the coupone code.

Schema

Customer:

• id (primary key)
• name (str)
• created_at (date, auto)

Coupon:

• id (primary key)
• created_at (date, auto)
• code (unique str)
• description (str)
• discount (float)
• discount_type (enum)
• customer (optional, foreign key)
• valid_from (date)
• valid_until (date)

Note: having customer in Coupon means a coupon can be used either by a single customer or by anyone. Supporting "group" coupon would require an additional link table (and the removal of the customer attribute).

Configuration

Configuration requires python-dotenv and is done with pydantic.Settings.

PostreSQL

Database driver: psycopg2-binary

After a local PostgreSQL install, you will need to create a database user or alter the default postgres user for example like this (from the psql console that can be started with sudo -u postgres psql):

ALTER USER postgres PASSWORD '<your-password>';

You will also need to create a database, for example with this command:

SELECT 'CREATE DATABASE <databasename>'
WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'databasename')\gexec

CLI

Built with typer.

Execute with python -m app_cli.main.

Run demo fixture: python -m app_cli.main demo.

Testing

TODO

Development

Dependencies: fastapi[all] sqlmodel typer[all].

Linting and formatting: black mypy ruff.

Testing: pytest.

Dependency management

Currently pipenv, probably moving to poetry in the future.