One thing I’d add to this is that your database schema and your UI data model and/or API are decoupled so you can update your front end to the new representation before you do any database changes.

One thing I liked was the chosen example is changing Booleans to enums. This almost always happens. Your field is almost never a Boolean. This goes for code too. We’ve all read code like:

    foo(false, false, true, null);

This leads to coding standards that all such parameters must be commented and breakages when the parameter list is changed. It also often results in hacks to squeeze a third value into your Boolean (eg Optional<Boolean>).

Or, my favorite:

    @nullable Optional<Boolean>

As I like to say: for when three values for your Boolean just aren’t enough.

So yeah, my tip for the day is just make any Boolean an enumeration from the outset.