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copied!<p>I'm taking a bit of a wild shot here, because I didn't refactor too much data in my life. </p> <p>You're making a strange comparison: If you wanted to 'hot-migrate' the db, you'd probably have to do the <code>x+1</code>, <code>x+2</code> versioning approach you described, but I don't really know - I wouldn't know how to do this with SQL either since I'm not a db expert.</p> <p>If you're migrating 'cold', however, you could just do it in one step by instantiating a new object from the old data, store the new object, delete the old object for each object in the store. See <a href="http://developer.db4o.com/Documentation/Reference/db4o-7.4/net2/reference/html/reference/implementation_strategies/refactoring_and_schema_evolution/refactoring_class_hierarchy/removing_class_from_a_hierarchy.html" rel="nofollow noreferrer">db4o reference</a>.</p> <p>But honestly: the same process in a RDBMS is complicated, too, because you will have to de-activate constraint checks (and possibly triggers, etc.) to actually perform the operation - perhaps not in the example you provided, but for most real-world cases. After all, the string split is so easy that there will be little gain.</p> <blockquote> <p>In SQL I would simply populate "first_name" and "second_name" columns</p> </blockquote> <p>Yes, with a <em>simple</em> string split operation, you can <em>simply</em> do that. But in a typical refactoring scenario, you're re-structuring objects based on large and complicated sets of rules that might not be easily expressed in SQL, might need complex calculation, or external data sources. </p> <p>To do that, you'd have to write code, too.</p> <p>After all, I don't see too much difference in the two processes. You will always have to be careful with live data, and you will certainly make a backup in both cases. Refactoring is fun, but persistence is tricky so synchronizing it is a challenge in any case. </p>

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