peewee migration

README.md

peewee migration notes

Peewee orm has built-in migration but it is not full-featured as of peewee 3.16.0.

It's missing:

1. state tracking table that can track what's been applied
2. auto-generate migrations
3. the migrator doesn't have create table I think

These are my future-reference notes to myself documenting the minimal thing I built to solve the first problem above.

There are third-party libraries for generating + running peewee migrations; I have not checked them out, but if you are shopping, you should.

This isn't designed to be comprehensive or even reliable / safe, it's a minimal implementation to get a low-risk project into production.

migrate.py

import logging
from peewee import fn
from playhouse.migrate import SqliteMigrator, migrate
from models import db, SomeModel, MODELS, Migrations

logger = logging.getLogger(__name__)
migrator = SqliteMigrator(db)

def short_add(model, name):
    "DRY migrator.add_column helper"
    return migrator.add_column(model._meta.table_name, name, getattr(model, name))

# list of all migrations
migs = [
    short_add(SomeModel, 'name'),
]   
    
def run_missing_migrations():
    db.connect()
    schema_exists = Migrations.table_exists()
    db.create_tables(MODELS, safe=True)
    if not schema_exists:
        logger.info('no migrations table, setting initial migration')
        Migrations.insert(id=len(migs)).execute()
    else:
        max_index, = Migrations.select(fn.MAX(Migrations.id)).execute()
        remaining_migs = migs[max_index.id:]
        logger.info('max mig %d, total %d, applying %d', max_index.id, len(migs), len(remaining_migs))
        migrate(*remaining_migs)

models.py

from peewee import SqliteDatabase, Model, DateTimeField, SQL, CharField
from playhouse.sqlite_ext import AutoIncrementField

db = SqliteDatabase('FILENAME.sqlite')

class Base(Model):
    id = AutoIncrementField()
    created = DateTimeField(constraints=[SQL('default current_timestamp')])

    class Meta:
        database = db

class Migrations(Base):
    "this tracks migrations that have been applied"
    pass

class SomeModel(Base):
    name = CharField()