datetime - How do I tell if a given NaiveDateTime (plus timezone like "US/Mountain") is in the past in Elixir?

Question

Suppose I have ndt of type NaiveDateTime and a string tz like "US/Mountain". How can I find out if ndt in tz is in the past?

question from:https://stackoverflow.com/questions/65890851/how-do-i-tell-if-a-given-naivedatetime-plus-timezone-like-us-mountain-is-in

Answer 1

Elixir doesn't include a timezone database by default, but it does support timezones if you add one. The easiest way is to use Tzdata.

1. Add {:tzdata, "~> 1.1"} to mix.exs
2. Add config :elixir, :time_zone_database, Tzdata.TimeZoneDatabase to config/config.exs
3. Use DateTime.from_naive!/3 to convert to a timezone-aware DateTime.
4. Use DateTime.compare/2 to compare the date to now.

~N[2000-01-01 10:10:10]
|> DateTime.from_naive!("US/Mountain")
|> DateTime.compare(DateTime.utc_now())
|> Kernel.==(:lt)

Output:

true

---

Config example:

# config/config.exs
import Config
config :elixir, :time_zone_database, Tzdata.TimeZoneDatabase