[SolarNet]

Temporary development functionality, not permanent (I said "as you make schema swaps").

> keep the code and the database functionality in sync.

At any time there should only be a fixed number of versions of the code (ideally two: Production and Stage; and maybe a half, Development, if things go really sour). Hence the overhead for supporting that fixed number of versions should then be relatively constant. When a system is done and moved to maintenance mode you remove all of your temporary functionality and get the database back to it's optimal form for the current code.

Obviously it gets tricky when you are doing multiple products on the same database, or a very large database. But I don't see how a DAL delivers anything to those that just having clean well documented code and using existing database features doesn't.

Stable App w/ old schema -> add functionality to support new schema -> add new code w/ new schema -> add functionality to support old schema, migrate to new schema -> remove old app w/ old schema -> remove now vestigial functionality supporting old schema. Supports multiple versions of the code and supports rolling updates. If it's hard to keep track of that I don't know how to help you.