Fastapi Patterns

This is a comprehensive reference for structuring production FastAPI applications with modern Python patterns. It covers the full stack: app factories with lifespan management, pydantic-settings for configuration, proper dependency injection with type annotations, transactional service layers that separate business logic from routes, and SQLAlchemy async sessions. The code samples are complete and opinionated, showing real implementations of JWT auth, CORS middleware, Pydantic v2 validators, and pagination. Use this when you're past the tutorial phase and need to see how the pieces fit together in a maintainable codebase. The service layer pattern alone will save you from tangled route handlers.

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last updated: Aug 21, 2026

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Install

$ npx -y skills add affaan-m/ecc --skill fastapi-patterns --agent claude-code

Installs into .claude/skills of the current project.

Files

FastAPI Patterns

Modern, production-grade FastAPI development: project layout, Pydantic v2 schemas, dependency injection, async patterns, auth, transactional service methods, and testing.

Project Structure

my_app/
|-- app/
|   |-- main.py               # App factory, lifespan, middleware
|   |-- config.py             # Settings via pydantic-settings
|   |-- dependencies.py       # Shared FastAPI dependencies
|   |-- database.py           # SQLAlchemy engine + session
|   |-- routers/
|   |   `-- users.py
|   |-- models/               # SQLAlchemy ORM models
|   |   `-- user.py
|   |-- schemas/              # Pydantic request/response schemas
|   |   `-- user.py
|   `-- services/             # Business logic layer
|       `-- user_service.py
|-- tests/
|   |-- conftest.py
|   `-- test_users.py
|-- pyproject.toml
`-- .env

App Factory and Lifespan

# app/main.py
from contextlib import asynccontextmanager
from fastapi import FastAPI
from fastapi.middleware.cors import CORSMiddleware

from app.config import settings
from app.database import engine, Base
from app.routers import users

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