fastapi-backend-architecture

To prevent transaction leakage in a FastAPI backend, enforce a strict layered architecture where HTTP routes remain transport-only, services hold business logic, and repositories interact with the database using flush-and-refresh update semantics while keeping transaction commit and rollback confined to a centralized session manager.

The best way to avoid leaking ORM models in FastAPI services is to mandate Pydantic DTOs for all service inputs and outputs, stabilizing service contracts and ensuring database models remain isolated within the repository layer.

To add a FastAPI endpoint while preserving module isolation, use dependency provider wiring for services and repositories, define DTO-based service contracts, keep services transaction-unaware, and include tests following a strict mocking matrix where routers mock services and services mock repositories.

Yes, you can use HTMX with FastAPI in a layered architecture by applying decorator-based patterns and specific response semantics for HTMX-driven view endpoints, ensuring they remain integrated within the isolated module structure.

FastAPI backends develop blurred layer responsibilities and inconsistent testing boundaries when lacking strict route, service, and repository separation, centralized transaction management, and a defined mocking matrix where router tests mock services and service tests mock repositories.

Yes, SQLAlchemy is required to manage transactions in this layered FastAPI architecture, specifically by confining the transaction lifecycle—commit and rollback—within a dependency or session manager and prescribing flush-and-refresh semantics inside repositories.