From shifted DateTime to Cldr.DateTime.to_string/2

Questions / Help
,
1

I have a UTC datetime from a timestamptz PostgreSQL column, and am trying to:

  1. convert it to the user’s timezone;
  2. output a localised string representation for the frontend.

I’m trying to use DateTime for 1 and Cldr.DateTime for 2.

iex> {:ok, shifted} = DateTime.shift_zone(~U[2024-07-13 21:33:23.163097Z], "Europe/Berlin")
{:ok, #DateTime<2024-07-13 23:33:23.163097+02:00 CEST Europe/Berlin>}

However, Cldr.DateTime.to_string/2 doesn’t accept #DateTime<...>:

iex> {:ok, result} = Cldr.DateTime.to_string(shifted, "en-GB")
** (MatchError) no match of right hand side value: {:error, {ArgumentError, "Invalid DateTime. DateTime is a map that contains at least :year, :month, :day, :hour, :minute, :second and :calendar. Found: #DateTime<2024-07-13 23:33:23.163097+02:00 CEST Europe/Berlin Cldr.Calendar.Gregorian>"}}
    (stdlib 4.3.1.3) erl_eval.erl:496: :erl_eval.expr/6
    iex:3: (file)

I don’t know what #...<...> means, exactly, or how to convert it to a DateTime struct/map that Cldr.DateTime can use. Thanks.

1 Like
2

Looks like you are calling Cldr.DateTime.to_string incorrectly.

The locale must be passed as a keyword list. This should work:

{:ok, result} = Cldr.DateTime.to_string(shifted, locale: "en-GB")
3

:face_with_peeking_eye: Thanks.

So the #...<...> syntax is an alternative representation of a struct? I tried searching for information on that, but I must have done that wrong, too.

4

It’s simply human-friendly formatting, suitable for quickly taking a look.

5

See Inspect — Elixir v1.12.3

6

I’ve published ex_cldr_dates_times version 2.20.2 that improves the error message when options are not provided as a keyword list. Using your example:

iex> {:ok, shifted} = DateTime.shift_zone(~U[2024-07-13 21:33:23.163097Z], "Europe/Berlin")
{:ok, #DateTime<2024-07-13 23:33:23.163097+02:00 CEST Europe/Berlin>}

iex> Cldr.DateTime.to_string(shifted, "en-GB")
{:error,
 {ArgumentError,
  "Unexpected option value \"en-GB\". Options must be a keyword list"}}
5 Likes
7

@dimitarvp, @LostKobrakai, thanks. So the use of # seems to be related to a comment marker, as the representation is not valid Elixir syntax. In 1.17’s documentation: Inspect — Elixir v1.17.2. That mentions that #Name<...> tends to be used when there are private fields to hide. I guess in the case of DateTime it’s used for conciseness.

@kip, thanks, and thanks very much for your libraries!