There are few libraries to interface with database in general, and there is not ORM library.
RMySQL is useful, but you have to write the SQL queries manually and there is not a way to generate them as in a ORM. Morevoer, it is only specific to MySQL.
Another library set that R still doesn't have, for me, it is a good system for reading command line arguments: there is R getopt but it is nothing like, for example, argparse in python.
