Error when creating Ecto User Type

Phoenix Forum Questions / Help
,
1

I have a record that contains :naive_datetime field
I want to save he value in GMT timezone but display it in Asia/Jerusalem timezone
so, I created the type like this

defmodule Jot.DatetimeType do
  @moduledoc false
  use Ecto.Type
  def type, do: :naive_datetime

  def load(tim) do
    # Convert GMT time to local time
    tim = DateTime.from_naive!(tim, "GMT")
          |> Timex.Timezone.convert("Asia/Jerusalem")
    {:ok, tim}
  end

  def dump(:naive_datetime = datetime) do
    {:ok, Timex.parse!(datetime, "{YYYY}-{0M}-{0M} {h24}:{0m}")}
  end

  def dump(_), do: :error

  def cast(datetime) when is_binary(datetime) do
    {:ok, Timex.parse!(datetime, "{YYYY}-{0M}-{0M} {h24}:{0m}")}
  end


# This is the problematic function
#=============================
  def cast(datetime) do
    datetime = DateTime.from_naive!(datetime, "Asia/Jerusalem")
          |> Timex.Timezone.convert("GMT")
    {:ok, DateTime.to_naive(datetime)}
  end


end

When I want to update the record like this:

Presence.update_entry_tran(t, %{punch_date: d})

I am getting an error

(Ecto.ChangeError) value `~N[2021-10-19 15:02:00]` for `Jot.Presence.EntryTran.punch_date` in `update` does not match type Jot.DatetimeType

Any idea?

2

I’d probably only operate on UTC datetimes in the model layer and move timezone logic to the view layer.

As for the timezone logic itself, you can transform a naive datetime to a datetime with timezone with DateTime.from_naive and optional DateTime.shift_zone.

Also you probably have a typo in the dump function, def dump(:naive_datetime = datetime) do would never match a naive date time struct, and if you have a datetime struct coming into a dump/1 function, you don’t need to modify it in any way since postgrex knows how to encode it.

3

I don’t want to move the logic to the view. I know that I will use it in more then 1 view, and I want it to convert automatically

4

Try this then:

defmodule Jot.DatetimeType do
  @moduledoc false
  use Ecto.Type

  @impl true
  def type, do: :naive_datetime

  @impl true
  def cast(datetime) when is_binary(datetime) do
    # if Timex.parse! fails to parse a raw datetime, it would raise an exception and crash the process
    # instead, a non-raising version should be used for the failed cast to be turned into an error in a changeset
    with {:error, _reason} <- Timex.parse(datetime, "{YYYY}-{0M}-{0M} {h24}:{0m}") do
      :error
    end
  end

  def cast(%NaiveDateTime{} = naive) do
    # you can do timezone shifting here as well
    {:ok, naive}
  end

  def cast(%DateTime{} = datetime) do
    {:ok, datetime}
  end

  @impl true
  def load(%NaiveDateTime{} = naive) do
    jerusalem =
      naive
      |> DateTime.from_naive!("Etc/UTC")
      |> DateTime.shift_zone!("Asia/Jerusalem")

    {:ok, jerusalem}
  end

  @impl true
  def dump(%NaiveDateTime{} = naive) do
    {:ok, naive}
  end

  def dump(%DateTime{} = jerusalem) do
    naive =
      jerusalem
      |> DateTime.shift_zone!("Etc/UTC")
      |> DateTime.to_naive()

    {:ok, naive}
  end
end
2 Likes
5

Thanks. Its working now