django-syzygy 0.1.0a1

Installation

pip install django-syzygy

Usage

Add ‘syzygy’ to your INSTALLED_APPS

# settings.py
INSTALLED_APPS = [
    ...
    'syzygy',
    ...
]

Setup you deployment pipeline to run migrate –pre-deploy before rolling out your code changes and migrate afterwards to apply the postponed migrations.

Concept

Syzygy introduces a notion of prerequisite and postponed migrations with regards to deployment.

A migration is assumed to be a prerequisite to deployment unless it contains a destructive operation or the migration has its stage class attribute set to POST_DEPLOY. When this attribute is defined it will bypass operations based heuristics.

e.g. this migration would be considered a prerequisite

class Migration(migrations.Migration):
    operations = [
        AddField('model', 'field', models.IntegerField(null=True))
    ]

while the following migrations would be postponed

class Migration(migrations.Migration):
    operations = [
        RemoveField('model', 'field'),
    ]

from syzygy import Stage

class Migration(migrations.Migration):
    stage = Stage.POST_DEPLOY

    operations = [
        RunSQL(...),
    ]

In order to prevent the creation of migrations mixing operations of different stages this package registers system checks. These checks will generate an error for every migration with an ambiguous stage.

e.g. this migration would result in a check error

class Migration(migrations.Migration):
    operations = [
        AddField('model', 'other_field', models.IntegerField(null=True)),
        RemoveField('model', 'field'),
    ]

Migration revert are also supported and result in inverting the nature of migrations. A migration that is normally considered a prerequisite would then be postponed when reverted.

With this new notion of migration stage it’s possible for the migrate command to target only migrations meant to be run before a deployment using the –pre-deploy flag or error out in the case on an ambiguous plan.

Development

Make your changes, and then run tests via tox:

tox