> 2. How do people (in general) and how do object-relational mappers (in > particular) deal with changing data models?
I've seen several people/projects query the data store for its schema version at app startup, and when the code is newer, run an ordered series of code patches that incrementally upgrade the schema and do the corresponding data conversions. Normally, the patchers are largely SQL scripts, but code scripts that perform complex processing or other IO are sometimes necessary. The one golden rule is taht you can't use make instances of your persistent objects in the upgraders as at that particular time the data store schema will be older than the schema assumed by the code and things will break.
Pete
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