121: Data Types: DateTimes Part 4.

Dates and times are a lot more complicated than we normally realize. This episodes explains durations. You can specify a duration directly and it’s very simple now that you know how the date and time portion works. Just like how a capital letter T is used to signal the beginning of a time, a duration uses a capital letter P. The P stands for period. And there are two ways you can express a duration. In the first method, you can include numeric values for a number of years, months, days, hours, minutes, and seconds just like how you would specify a date or time. But instead of a fixed number of digits, this form of a duration places another capital letter after each field. You can leave out fields if they’re zero or if you just don’t need them. After the years, place a capital Y. After the months, place a capital M. After the days, place a capital D. After the hours, place a capital H. After the minutes, place a capital M. And after the seconds, place a capital S. You can instead refer to a duration of weeks and then use a capital letter W. You can’t combine weeks with the other fields though. So if you’re using weeks, then you can only use weeks. Notice how both months and minutes both use a capital M? That’s okay because you still need the capital letter T to be placed before any time fields. Using this form of a duration, if you want to express 10 hours and 30 minutes, then the proper way to do this is by writing: PT10H30M. What if you want a duration of 15 months, 1 day, and 12 hours? This is an interesting example because it shows a unique feature of durations that isn’t allowed in the normal DateTime representation. You’re allowed to exceed the normal range of fields in a duration. You can represent 15 months, 1 day, and 12 hours in a few different ways. You can first convert 15 months into years and months like this: P1Y3M1DT12H Or you can just use the months as-is even though it goes beyond 12 like this: P15M1DT12H And you can still make use of fractional values at any point. Once you use fractional values though, there can be no more fields. You can combine the 12 hours into half a day like this: P15M1.5D The second form of expressing a duration uses the representation of a DateTime. Using what I just explained about the extra capital letters, you can still use all the date and time formatting you already know to represent a duration by just placing a capital P before it. So you can also represent 10 hours and 30 minutes like this: PT10:30 Listen to the full episode for further explanation or you can also read the full transcript below. Transcript This episode continues the explanation of DateTime data types. I want to go back and explain a topic better that I introduced in episode 119, DateTimes, Part 2. In that episode, I asked what 10:30 means. Is that a specific point in time or 10 hours and 30 minutes. And I said that it was up to you to decide. It wasn’t really a duration that I wanted to explain. In a way it was. But this episode will explain durations better than that. Real durations. I should not have said 10 hours and 30 minutes because that’s a real duration. The type of duration I was thinking about was an implied duration based on the precision of the DateTime. In other words, does 10:30 mean the exact point in time at 10 hours and 30 minutes into some day? Or does it cover the entire minute between 10:30 and 10:31? Normally, when I see something like 10:30, I think of the exact point in time. The same thing applies to a date. Does 2020 refer to the moment on zero hours January 1st, 2020 only? Or does it refer to the entire year. I normally use dates like this to refer to the entire duration specified. But when you think about it, a DateTime is really just a value that can be as precise as you want by including ever smaller units from years, to months, to days, then to hours, minutes, seconds, and fractional values at any point along the way. So