How to convert Date to DateTime which Ecto needs

Questions & Help Questions
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1

Hello, I get Persian date from my client and convert it to normal calendar like this:

  def jalali_string_to_miladi_english_number(persian_string_time_number) do
    [yy, mm, dd] = String.split(persian_string_time_number, "/")
    {:ok, jalaali_date} = Date.new(Numero.normalize_as_number!(yy), Numero.normalize_as_number!(mm), Numero.normalize_as_number!(dd), Jalaali.Calendar)
    {:ok, iso_date} = Date.convert(jalaali_date, Calendar.ISO)
    iso_date
  end

my output is:

~D[2019-05-21]

but I can’t save this in my database and have this error:

value `~D[2019-05-21]` for `TransactionSchema.purchase_time` in `insert` does not match type :utc_datetime

how can convert it to utc_datetime can be saved in db with ecto like this DateTime.utc_now ?

Thanks