postcar 0.0.3

A database migration utility for Postgres

postcar

---

Table of Contents

• Installation
• License

Installation

pip install postcar

License

postcar is distributed under the terms of the Apache-2.0 license.

Usage

Migrations

Migration packages

Each migration package needs to be importable. Migration modules must be named starting with a four digit sequence number, followed by an underscore, and a (short) description.

Here's a sample structure of a migration directory:

migrations
├── __init__.py
├── 0001_init.py
├── 0002_authorization.py
└── 0003_create_extensions.py

Migration modules

The migration modules must contain a class named Migration, which must inherit from postcar.Migration.

A minimal migration file might look as follows:

import postcar


class Migration(postcar.Migration):
    def get_forward(self) -> str:
        return """
            create extension pg_trgm;
        """

    def get_rollback(self) -> str:
        return """
            drop extension pg_trgm;
        """

CLI

The package comes with a minimal CLI.

See python -m postcar --help for available commands.

Configuration

NOTE: this isn't implemented yet, so use the CLI for the time being

Sample configuration file:

# postcar.conf.py

import os
from postcar import config


connection = config.ConnectionInfo(
    host="127.0.0.1",
    port=5432,
    dbname="mydb",
    username="postcar",
    password=os.getenv("POSTGRES_PASSWORD"),
)

namespace = "_bookkeeping"

packages = ["myapp.migrations"]

Configuration parameters

The below table is an exhaustive list of the available parameters. More detailed descriptions below the table.

Name	CLI	Type	Default
—	-c/--conf	Optional[str]	None
connection.host	-H/--host	Optional[str]	None
connection.port	-p/--port	Optional[int]	None
connection.dbname	-D/--dbname	Optional[str]	None
connection.username	-U/--user	Optional[str]	None
connection.password	-P/--password	Optional[str]	None
namespace	-s/--namespace	str	"_postcar"
packages	—	Sequence[str]	()

connection.[x]

Connection info parameters, very similar to the Postgres defaults.

namespace

The database schema to use for bookkeeping.

packages

The migration packages to run migrations for by default.

Development

Internal migrations

For the sake of consistency, and keeping things "simple", internal schema migrations are designated by minor versions. In short, a bump from 1.2.3 to 1.2.4 must never migrate the internal schema, whereas 1.2.3 to 1.3.0 or 2.0.0 may.

Ultimately, the goal is to enable effortless upgrades between versions, without unnecessarily complicated manual intervention.

Regardless: this is a rather experimental package, at least until version 1.0.0. Until then: expect things to break, without any guarantees.

TODO

• Implement rollback
• Migration dependencies
• CLI command for generating a new migration skeleton