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Django migration linter

Detect backward incompatible migrations for your django project. It will save you time by making sure migrations will not break anything.

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Installation

pip install django-migration-linter

Usage

Add the migration linter your INSTALLED_APPS:

INSTALLED_APPS = [
    ...,
    "django_migration_linter",
    ...,
]

python manage.py lintmigrations [GIT_COMMIT_ID] [--ignore-name-contains IGNORE_NAME_CONTAINS] [--include-apps INCLUDE_APPS [INCLUDE_APPS ...] | --exclude-apps EXCLUDE_APPS [EXCLUDE_APPS ...]] [--exclude-migration-tests MIGRATION_TEST_CODE [MIGRATION_TEST_CODE ...]] [--project-root-path DJANGO_PROJECT_FOLDER]

Parameter Description
GIT_COMMIT_ID If specified, only migrations since this commit will be taken into account. If not specified, all migrations will be linted.
--ignore-name-contains IGNORE_NAME_CONTAINS Ignore migrations containing this name.
--ignore-name IGNORE_NAME [IGNORE_NAME ...] Ignore migrations with exactly one of these names.
--include-apps INCLUDE_APPS [INCLUDE_APPS ...] Check only migrations that are in the specified django apps.
--exclude-apps EXCLUDE_APPS [EXCLUDE_APPS ...] Ignore migrations that are in the specified django apps.
--exclude-migration-tests MIGRATION_TEST_CODE [...] Specify backward incompatible migration tests to be ignored using the code (e.g. ALTER_COLUMN).
--verbose or -v Print more information during execution.
--database DATABASE Specify the database for which to generate the SQL. Defaults to default.
--cache-path PATH specify a directory that should be used to store cache-files in.
--no-cache Don't use a cache.
--applied-migrations Only lint migrations that are applied to the selected database. Other migrations are ignored.
--unapplied-migrations Only lint migrations that are not yet applied to the selected database. Other migrations are ignored.
--project-root-path DJANGO_PROJECT_FOLDER An absolute or relative path to the django project.

Examples

3YOURMIND is running the linter on every build getting pushed through CI. That enables to be sure that the migrations will allow A/B testing, Blue/Green deployment and they won't break your development environment. As every reasonable tool, a non-zero error code means that at least one invalid migration has been found.

Backward incompatible migrations

The linter analyses your migrations and checks the SQL for:

  • Added NOT NULL columns, which don't have a DEFAULT value
  • Dropping columns
  • Dropping tables
  • Renaming columns
  • Renaming tables
  • Altering columns (which can be backward compatible and potentially ignored)
  • Adding a unique constraint

Those are the most important and frequent backward incompatible migrations. We are happy to add more if you can specify them to us.

Ignoring migrations

You can also ignore migrations by adding this to your migrations:

import django_migration_linter as linter
# ...

    operations = [
        linter.IgnoreMigration(),
        # ...
    ]
# ...

Ignoring migration tests

You can also ignore backward incompatible migration tests by adding this option during execution:

python manage.py lintmigrations --exclude-migration-tests ALTER_COLUMN

The migration test codes can be found in the file django_migration_linter/sql_analyser.py.

Cache

By default, the linter uses a cache to prevent linting the same migration multiple times. The default location of the cache on Linux is /home/<username>/.cache/django-migration-linter/<version>/<ldjango-project>_<database_name>.pickle.

Since the linter uses hashes of the file's content, modifying a migration file will re-run the linter on that migration. If you want to run the linter without cache, use the flag --no-cache. If you want to invalidate the cache, delete the cache folder. The cache folder can also be defined manually through the --cache-path option.

Tests

The easiest way to run the tests is to invoke tox.

You will need to install the test requirements, which can be found in the setup.py file. A good way to get started is to install the development version of the linter by doing pip install -e .[test].

To be able to fully test the linter, you will need both MySQL and PostgreSQL databases running. You can either tweak the tests/test_project/settings.py file to get your DB settings right, or to have databases and users corresponding to the default Travis users.

Contributing

First, thank you very much if you want to contribute to the project. Please base your work on the master branch and also target this branch in your pull request.

Publishing the package

A small note on how the linter is usually published to PyPi:

  • python setup.py check --restructuredtext
  • python3 setup.py sdist bdist_wheel --universal
  • twine upload dist/django_migration_linter-X.Y.Z-py2.py3-none-any.whl dist/django-migration-linter-X.Y.Z.tar.gz

Blog post

Keeping Django database migrations backward compatible

License

django-migration-linter is released under the Apache 2.0 License.