Objects are serialized to a database using the .NET XML serializer. The object can change over time, and therefore multiple versions exist in the database at one time.
Any suggestions for the best way to construct your code, so that you can still deserialize this object into the latest version. (interfaces / maps / manual serialization etc.)
Don't remove/rename properties. Only add them.
Assign default values to all properties.
This will guarantee that xml serializer will be able to deserialize old xml into new object, and that object will have "sane" values.
What Alex Reitbort tells.
You can also implement the ISerializable interface to handle old value's
Have a schema version number in the serialized object. Using custom deserialization, check the version attribute first, and if it turns out to be an old version, upgrade it to the latest schema before deserializing.
Look here this talk about best practices on WCF datacontract versioning, this is a bit more specific than what you really want, but these patterns solve the same problem as yours, you can use them in any technology you want.
This all depends on your application. Is it a distributed rich application where old applications may encounter new data objects from a central database or other source? (Much like older versions of office applications need to have some ways of dealing with newer document formats.)
If so, custom serialization and deserialization with explicit schema version numbering, I'd say. I'd put explicit metadata on each element and attribute, stating whether a reader must understand the element/attribute (and default values if not). This can of course consume quite a lot of space and increase code complexity...
But the answer really depends on why you are serializing to a database. You're not interested in using the database for its relational capabiities? Otherwise, an O/R mapping solution might be of interest.