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FastAPI Users + SQLModel Integration Example

A minimal example demonstrating how to integrate FastAPI Users (SQLAlchemy) with SQLModel for user authentication and cross-model database relationships.

Overview

This example covers:

  • Using SQLAlchemy User model (required by FastAPI Users) alongside SQLModel entities
  • Defining relationships across SQLAlchemy and SQLModel models
  • Running Alembic migrations in a mixed setup

Quick Start

Prerequisites

  • Python 3.13+
  • uv package manager

Setup

  1. Install dependencies:

    uv sync
source .venv/bin/activate

  2. Initialize the database:

    alembic revision --autogenerate -m "Initial migration"
alembic upgrade head

  3. Create sample data:

    python create-sample-data.py

  4. Start the server:

    python main.py

  5. Test the API:

    # Get users (SQLAlchemy) in a group (SQLModel)
curl http://localhost:8000/user-groups/1/users

Project Structure

fastapi-users-sqlmodel-example/
├── app/
│   ├── __init__.py
│   ├── app.py              # FastAPI application & routes
│   ├── db.py               # Database connection & session
│   ├── models.py           # SQLAlchemy + SQLModel models
│   ├── schemas.py          # Pydantic schemas
│   └── users.py            # FastAPI Users configuration
├── alembic/                # Database migrations
├── alembic.ini             # Alembic configuration
├── create-sample-data.py   # Sample data creation script
├── main.py                 # Application entry point
├── pyproject.toml          # Project dependencies
└── README.md

Important Differences From SQLAlchemy Example

Alembic Setup

  • Set sqlalchemy.url in alembic.ini to a sync URL: sqlite:///./test.db
  • Add the following to alembic/env.py:
from app.models import SQLModel

target_metadata = SQLModel.metadata
  • Add the following to alembic/script.py.mako:
import fastapi_users_db_sqlalchemy
import sqlmodel.sql.sqltypes

Model Integration (app/models.py)

  • Bind SQLModel to SQLAlchemy’s shared metadata and class registry:
    • SQLModel.metadata = Base.metadata
    • SQLModel._sa_registry = Base.registry
  • Add a relationship between User (SQLAlchemy) and UserGroup (SQLModel)

Database Session Management (app/db.py)

  • Use SQLModel's AsyncSession instead of SQLAlchemy's
  • Remove the create_db_and_tables function in favor of Alembic

Application Routes (app/app.py)

  • Remove the lifespan event that creates tables, since Alembic is used
  • Add the /user-groups/{group_id}/users endpoint to demonstrate the relationship between SQLAlchemy and SQLModel models