Ruby on Rails

re: Data migrations

By separating your schema migrations from data migrations, you can separate the concerns easily. (And, for example, not run your data migrations in a test or QA environment if you so choose)

Also schema migrations necessarily mean you have to restart your app (downtime), and data-only migrations can be run while the app is running. 

Almost every production-scale website with traffic I've worked on has needed data migrations at some point. While making everything a data migration is costly to developers, doing it for batch imports makes perfect sense. Let's say your company acquired another company, and you wanted to import the other company's data. Yes, you could reasonably use a rake task, but data migrations make it easy to keep track of and ensure that all environments get the same treatment.

Although I understand the sentiment that it "smells bad" (and indeed, running a large data job in a schema migration can take a while, leaving your site down during the migration), the purpose of my gem is to address a real business need in a way that isn't so smelly to developers. In the context of this discussion, I'd call it a middle-ground approach.

-Jason