Converting "4:00AM" to ISO8601 - sql

Question

The frontend is sending time values like "4:00AM" or "7:15PM" and I need to convert these to ISO8601 (i.e. "04:00:00" and "19:15:00" respectively) so that I can store them in a "time without time zone" column in PostgreSQL.
What is the easiest way to do this? I have Timex available, and am using Ecto.

Answer 1

Postgres is flexible about date and time formats. You can just cast these strings:
select '4:00AM'::time, '7:15PM'::time
time | time
:------- | :-------
04:00:00 | 19:15:00

Answer 2

In Postgres 'timestamp(tz), date, time(tz), etc` are not stored in a format. Formatting is something you do on retrieval. So:
create table time_test(time_fld time);
insert into time_test values ('4:00AM');
insert into time_test values ('7:15PM');
select time_fld from time_test ;
time_fld
----------
04:00:00
19:15:00
Just pass the string in and let Postgres do the work.

Answer 3

One might manually convert the value to the appropriate Time struct.
iex|1 ▶ [h, m, pm?] =
...|1 ▶ "4:00PM"
...|1 ▶ |> String.downcase()
...|1 ▶ |> String.split(~r/:|(?<=\d)(?=\D)/)
#⇒ ["4", "00", "pm"]
iex|2 ▶ m = String.to_integer(m)
iex|3 ▶ h =
...|3 ▶ if(match?("pm", pm?), do: 12, else: 0) + String.to_integer(h)
#⇒ 16
iex|4 ▶ Time.from_erl!({h, m, 0})
#⇒ ~T[16:00:00]