Godeps/_workspace/src/gopkg.in/mgo.v2/session.go
func (s *Session) DB(name string) *Database {
	if name == "" {
		name = s.defaultdb
	}
	return &Database{s, name}
}
func (s *Session) DB(name string) *Database {
	if name == "" {
		name = s.defaultdb
	}
	return &Database{s, name}
}
// DB returns a value representing the named database. If name
// is empty, the database name provided in the dialed URL is
// used instead. If that is also empty, "test" is used as a
// fallback in a way equivalent to the mongo shell.
//
// Creating this value is a very lightweight operation, and
// involves no network communication.