5. Dependency Injection

Use FastAPI's Depends system to share DB sessions, authentication, and reusable logic across routes.

📄️Dependencies Basics

Use FastAPI's Depends() to inject shared logic — database sessions, pagination parameters, and common headers — into route handlers.

Build composable, testable dependency functions for database access, authentication, feature flags, and external service clients.

Apply dependencies to entire routers or the entire application using router-level and app-level dependency lists.