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And you have to weaken your schema to allow nulls for the duration that old and new code are both running (and possible foreign key constraint failures).

Thanks. I thought it would be something... smarter. Not sure I like that, seems to come with a lot of caveats.

"smarter" means more code and that's rarely more maintainable.

It's what you have to do if you want less downtime. Normally it shouldn't span much more than 2-3 versions of application and it's rare that the annoying kind (say writing same data to "old" and "new" column) happens.

> until all your old application code is no longer running.

Or until it's been disabled by feature flags.