migri 0.5.0

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migri

A simple Python async migration tool. You can use the CLI (run yourself or from a shell script) or import the exposed functions and run programatically. Currently supports PostgreSQL (asyncpg), SQLite (aiosqlite), and MySQL (aiomysql).

migri is currently in alpha and although unlikely, the implementation may change

Motivation

Using async database libraries is useful when a service/application is already using an async library. It's extra overhead to install a synchronous library just to run migrations. Practically speaking, though, there isn't much benefit to running migrations asynchronously since migrations must be applied synchronously. Besides, the number of migrations for a service is generally small.

Getting started

Install migri

pip install migri[mysql]
pip install migri[postgresql]
pip install migri[sqlite]

Create migrations

Create a migrations directory and add your migrations. Migrations are applied in lexicographical order (e.g. 0001_initial.sql then 0002_add_user_data.py and so on).

Currently .sql and .py files are supported. If you write a Python migration file, ensure that it contains an async function migrate. An instance of asyncpg's Connection class will be passed into the function.

async def migrate(conn) -> bool:
    await conn.execute("INSERT INTO categories (name) VALUES ($1)", "Animals")
    return True

Migrate

Run migri migrate. Provide database credentials via arguments or environment variables:

• --db-name or DB_NAME (required)
• --db-user or DB_USER
• --db-pass or DB_PASS
• --db-host or DB_HOST
• --db-port or DB_PORT

Other options:

• -d, --dialect or DB_DIALECT (mysql, postgresql, sqlite, note that currently only postgresql is supported. If not set, migri will attempt to infer the dialect (and library to use) using the database port.)
• -l, --log-level or LOG_LEVEL (default error)

When you run migrate, migri will create a table called applied_migration (if it doesn't exist). This is how migri tracks which migrations have already been applied.

Dry run mode

If you want to test your migrations without applying them, you can use the dry run flag: --dry-run.

Unfortunately, dry run mode does not work with SQLite at this moment. If you want to try to get it to work, see the issue.

Dry run mode also doesn't work w/ MySQL because DDL statements implicitly commit.

Migrate programmatically

Migri can be called with a shell script (e.g. when a container is starting) or you can apply migrations from your application:

from migri import apply_migrations, PostgreSQLConnection

async def migrate():
    conn = PostgreSQLConnection(
        "sampledb",
        db_user="user",
        db_pass="passpass",
        db_host="localhost",
        db_port=5432
    )
    async with conn:
        await apply_migrations("migrations", conn)

Testing

1. Set up local Python versions (e.g. pyenv local 3.7.7 3.8.3)
2. Run docker-compose up to start Postgresql.
3. Install nox with pip install nox.
4. Run nox.

Docs

Docstrings are formatted in the Sphinx format.

Todos

• Don't record empty migrations - warn user
• Add dry run mode for testing migrations
• Output migration results
• Test modules not found
• Test/handle incorrect migrate function signature (in migration Python files)
• Add colorful output 🍭 for enhanced readability
• Make error output more readable