churros-py / churros-migrator

FastAPI with SQLModel and Alembic for PostgreSQL Migrations

This project demonstrates how to set up a FastAPI application using SQLModel with a PostgreSQL database and handle database migrations using Alembic in a separate Docker container.

Project Structure

api/
├── __init__.py
├── models.py
├── migration_service/
│   ├── Dockerfile
│   ├── alembic.ini
│   ├── env.py
│   ├── requirements.txt
│   ├── entrypoint.sh
│   └── versions/
└── docker-compose.yml

Prerequisites

• Docker
• Docker Compose

Setup Instructions

Step 1: Build and Run the Docker Containers

Build and start the services defined in the docker-compose.yml file:

docker-compose up --build

Step 2: Project Dependencies

Ensure you have the necessary dependencies listed in the requirements.txt for both the FastAPI app and the migration service.

migration_service/requirements.txt

alembic
psycopg2
sqlmodel

Step 3: Alembic Configuration

migration_service/alembic.ini

Update the alembic.ini file with your database connection string:

sqlalchemy.url = postgresql+psycopg2://username:password@db/mydatabase

migration_service/env.py

Ensure your models are imported correctly in env.py:

from logging.config import fileConfig
from sqlalchemy import engine_from_config, pool
from sqlmodel import SQLModel

from alembic import context

config = context.config
fileConfig(config.config_file_name)

from app.models import MyModel1, MyModel2  # Import your models here

target_metadata = SQLModel.metadata

def run_migrations_offline():
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )

    with context.begin_transaction():
        context.run_migrations()

def run_migrations_online():
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection,
            target_metadata=target_metadata,
        )

        with context.begin_transaction():
            context.run_migrations()

if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

Step 4: Entrypoint Script

migration_service/entrypoint.sh

Create an entrypoint script to handle the migration process:

#!/bin/bash

# Wait for the database to be available
while ! nc -z db 5432; do
  echo "Waiting for database..."
  sleep 1
done

# Run Alembic migrations
alembic upgrade head

echo "Database migration completed."

Step 5: Create and Apply Migrations

Whenever you make changes to your models, follow these steps:

1. Generate a new migration script:

   docker-compose run migration alembic revision --autogenerate -m "Describe your changes"

2. Apply the migration:

   docker-compose run migration alembic upgrade head

Running the FastAPI Application

The FastAPI application will be accessible at http://localhost:8000.

Example FastAPI Endpoint

from fastapi import FastAPI
from sqlmodel import SQLModel, Field

app = FastAPI()

class MyModel1(SQLModel, table=True):
    id: int = Field(default=None, primary_key=True)
    name: str

@app.get("/")
def read_root():
    return {"message": "Hello, World!"}

License

This project is licensed under the MIT License.