[Izkata]

Django (python web framework) migrations have worked similar to this for well over a decade: You modify the models, then generate the migrations from the models and commit those.

The changes aren't generated on the fly at runtime because it can prompt you for things it suspects or can't figure out, for example if you rename a column the naive way would be an add+delete, which erases data. If the types are the same, it checks whether you wanted that or a rename, and generates the appropriate migration.