linking Iterators together in this manner is more efficient (and convenient) than reading out the contents of each Iterator into a List and creating a new Iterator.
The incremental database reverse engineering (DBRE) add-on allows you to create an application tier of JPA 2.0 entities based on the tables in your database. DBRE will also incrementally maintain your application tier if you add or remove tables and columns.
D. Johnson, and T. Jankun-Kelly. Proceedings of graphics interface 2008, page 163--168. Toronto, Ont., Canada, Canada, Canadian Information Processing Society, (2008)