/* Calendars and Fares are special: they are stored as joined tables rather than simple maps. */
String service_id = getStringField("service_id", true); // TODO service_id can reference either calendar or calendar_dates.
Service service = feed.getOrCreateService(service_id);
if (service.calendar != null) {
feed.errors.add(new DuplicateKeyError(tableName, row, "service_id"));
} else {
Calendar c = new Calendar();
c.service = service;
c.monday = getIntField("monday", true, 0, 1);
c.tuesday = getIntField("tuesday", true, 0, 1);