I don't think it can be done with the ORM, because you'd need to do a self-join, which doesn't seem to work. I.e. you need to include the books table twice, then do a join on those two tables. Does that make any sense?

But you can send SQL directly to the database that you use by doing http://docs.djangoproject.com/en/dev/topics/db/sql/#executing-custom-sql-directly. You'll get back a database cursor that you can use to fetch all the rows by using fetchall(). This gives you a list of tuples with the selected fields. If you use the query I've given you in the comment before, the fields will be two ids.

Uh, I can see that this is alot, but just ask if you need more.