Chapter 13, Persistence, pp. 147-152.  We now can list vacations from the DB.
Chapter 13, Persistence, pp. 152-154, "Adding Data".
Chapter 13, "Persistence".  Improved error logging when MongoDB is not running. Factored DB connection/initialization code into new module.
Chapter 13, "Persistence, pp. 154-156.  Using MongoDB for Session Storage.