With the support for CouchDB's revision attribute we have the first case where values are generated in the data store. The currently developed implementation performs a separate read of the record after an insert/update, in case a property is marked as @Generated.
In certain cases this read could be avoided when the generated values are returned by the write itself. Taking again CouchDB as example, the updated revision is part of the response document returned by a POST or PUT. This could be leveraged by changing the GridDialect#updateTuple() and updateAssociation() methods to return a Tuple with properties generated by the data store.