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>> Even in the case of projects using versioned objects, it still
>> means a SQL layer has to include functionality for both versions of
>> a particular schema change which itself is awkward.

That's not true. Nova doesn't have multiple models to straddle a
particular change. We just...

> It's simple, these are the holy SQL schema commandments:
> 
> Don't delete columns, ignore them.
> Don't change columns, create new ones.
> When you create a column, give it a default that makes sense.
> Do not add new foreign key constraints.

...do this ^ :)

We can drop columns once they're long-since-unused, but we still don't
need duplicate models for that.

--Dan