FastAPI Patterns Modern, production-grade FastAPI development: project layout, Pydantic v2 schemas, dependency injection, async patterns, auth, transactional service methods, and testing. Project Structure --- App Factory and Lifespan --- Configuration with pydantic-settings --- Pydantic Schemas (v2) --- Dependency Injection --- Router and Endpoint Design --- Service Layer Note on Database Design: Application-level unique handling requires an underlying unique database index (e.g., on your SQLAlchemy mapping attributes). Without underlying constraints, application layer error-catching cannot…