[ToDo]Tweaks

No - what I mean is that a unique-constraint can only be set once when the table is created - if you attempt to change the constraint after the first run, it will rightfully cause an integrity error. Therefore, all DB-level constraints can only be constants and not dependent on a deployment setting.

That is why the ToDo said "validator" and not "unique key" - a validator can be changed at any time (although of course you can still not enforce uniqueness in hindsight - that would require a data cleanup).

The validator is required anyway (otherwise invalid data in imports will cause db-level errors, and in postgres we can't skip these as they will halt the transaction on any error).

Besides, we shouldn't make constraints dependent on the assumption that migrate will be set to False after first run - either that is required and happens automatically, or it is an invalid assumption. And development instances do almost never have migrate=False, yet they need to work!