Data Migrations

Over the time, the data models and thus the underlying database schema is changing to adapt new features or resolve bugs. Unfortunately Django cannot automatically detect and resolve those changes and upgrade existing instances for us.

To solve this problem, EOxServer uses South for schema and data migration management.

What are migrations?

For the uninitiated, migrations (also known as ‘schema evolution’ or ‘mutations’) are a way of changing your database schema from one version into another. Django by itself can only do this by adding new models, but nearly all projects will find themselves changing other aspects of models - be it adding a new field to a model, or changing a database column to have null=True.

—from the South documentation


South needs to be initialized in every instance that wants to make use of the migration features.

Setting up South is quite easy, as all you need to do is install South (most easily via pip or easy_install), add it to the INSTALLED_APPS setting in and run python syncdb:


A complete guide on all installation and configuration options can be found here.

Creating Migrations

To benefit from South it is important that every change in the data models concerning the actual database structure is tracked by a migration definition. Fortunately, for most of the small changes these can be created automatically by using Souths command python schemamigration and passing the app names which have changes in their models.

A very good tutorial for South can be found here.

Performing a Migration

To use South for data migrations only one command needs to be executed: python migrate. This applies all necessary database schema changes to your database and converts all included data from the original schema to the new one. This command effectively replaces syncdb (apart from the initial call to setup South).