isDayBefore method
Implementation
bool isDayBefore(DateKey arg) {
const Duration oneDay = Duration(days: 1);
DateTime outerDateTime = DateTime(arg.year, arg.month, arg.day);
DateTime traveledOuterDateTime = outerDateTime.subtract(oneDay);
DateKey traveledOuterDateKey = DateKey(traveledOuterDateTime.year,
traveledOuterDateTime.month, traveledOuterDateTime.day);
return this == traveledOuterDateKey;
}