FastAPI Patterns Build production-ready async APIs with FastAPI's dependency injection and type system. Project Layout App Factory Dependency Injection Pydantic Models Router Patterns Background Tasks Error Handling Testing Anti-Patterns - Sync database calls — Always use async drivers (asyncpg, aiosqlite) - Business logic in routes — Extract to service layer for testability - No response models — Always define response model for API documentation - Global state — Use dependency injection, not module-level singletons - Missing validation — Pydantic models should validate all inputs - No lifes…