Formatting a time in Elixir

Question

I'm new to Elixir, trying to port a Rails API to Phoenix as a learning project.

I have a Postgres time field, which I've added to an Ecto scheme:

field :start_time, Ecto.Time

Problem: I'd like to output a 12-hour formatted version of a time such as 16:30 as a string: 4:30pm, for example. I have been having trouble finding an easy/standard way of doing this.

This is the closest I've yet come to a solution:

def format_time(time) do
  {:ok, {hours,minutes,y, z}} = Ecto.Time.dump(time)
  {hour, ampm} = Timex.Time.to_12hour_clock(hours)
  "#{hour}:#{minutes}#{ampm}"
end

This seems like a ridiculous and ridiculously long piece of code for something I imagine already has a more concise and standard implementation; in addition it has the problem of outputting 2:0pm instead of 2:00 pm – formatting the 0 with a trailing zero was additionally long and complicated piece of code that I was working on –– at which point I started feeling like things were going way off track.

Advice appreciated!

Answer 1

I had the same problem and using a library like Timex. That's my way how to handle dates. I don't know if there better work cases.

• Calendar for parsing and some functions.
• Calecto for using Calendar with Ecto

In this case you can use Calendar.Strftime for a formatted date/time string.

I hope it helps.

Answer 2

You can use the formatting facilities of timex since you're already using that, but first you need to change your Ecto.Time into a Timex.DateTime that can be formatted with those.

use Timex

{{0, 0, 0}, Ecto.Time.to_erl(time)}
|> Timex.Date.from
|> DateFormat.format!("{h12}:{0m} {am}")

Answer 3

You're using Timex, but not its format! method which allows for easy time and date formatting.

https://david.padilla.cc/posts/19-date-formatting-in-phoenix-elixir is a good write up on using Timex.

It looks like you might be able to do something like the following:

Timex.DateFormat.format!(time, "%H:%M%P", :strftime)

See https://github.com/bitwalker/timex/blob/master/lib/format/datetime/formatters/strftime.ex for the full list of formatting options.

Answer 4

A simple way to do it is to use strftime string formatting available in Calendar. Using Calecto you can even use the basic types such as Ecto.Time or Ecto.DateTime. This can be piped directly to Calendar's formatting, like so:

@ecto_struct.some_time |> Calendar.Strftime.strftime! "%I:%M%P"

Will result in:

"02:30pm"

All you have to do is add Calecto as a dependency:

defp deps do
  [ {:calecto, "~> 0.4.1"}, ]
end