Data + backend / Intermediate → advanced

Backend architecture and data integrity

Service boundaries, validation, transactions, migrations, concurrency, caching, and designing state changes that remain correct under failure.

backendtransactionsmigrationsconcurrencycache

01Separate responsibilities

HTTP layer: parse request, authentication, authorization, response formatting.
Domain/service layer: business rules and workflows.
Persistence layer: database queries/transactions.
External adapters: email, storage, payment, network, third-party APIs.

02Data integrity

Validation in Python improves user experience, but database constraints protect the data when multiple workers, scripts, migrations, or future code paths write concurrently.

03Migrations are code

bashAlembic/Flask-Migrate deployment checks

flask --app manage.py db upgrade
flask --app manage.py db current