What does a South datamigration do compared to a schemamigration?

Question

I recently began digging into the South documentation and discovered that it had two distinct types of migrations:

• schemamigration
• datamigration

As a result of my ignorance, I've always used schemamigrations for everything. In other words, even if I had something that was truly a "data migration", I'd simply used South's schemamigration to convert the data (with no apparent consequences).

As I read the documentation, I'm not seeing a fault in this approach. Does anyone know the fundamental difference between the two migrations and what I may be missing by sticking with schemamigrations?

Answer 1

There's really only one kind of migration, but two commands. datamigration creates a new blank migration for you to fill out, while schemamigration is an optional convenience command which will attempt to detect schema changes and create a migration automatically.

Edit: from http://south.aeracode.org/docs/commands.html#schemamigration

While migrate is the real meat and bones of South, schemamigration is by comparison an entirely optional extra. It’s a utility to help write some of your migrations (specifically, the ones which change the schema) for you; if you like, you can ignore it and write everything youself, in which case we wish you good luck, and happy typing.

Answer 2

Per the lead developer of South:

You can see the difference here: https://bitbucket.org/andrewgodwin/south/src/b3ed126b19a2/south/v2.py

As that shows, the only difference is that data migrations aren't dry-run if you have a database that requires it (MySQL). Otherwise, there's little difference, at least at the moment - the management commands differ, though (it's all about user interface separation, essentially).