#blog_snippets

week_may4_validation05.ex

def validate(changeset) do
  changeset
  |> validate_required([:revenue, :expense, :net_gain, :first_name])
  |> mathematical_validation()
  |> validate_format(:reference_id, ~r/(^\d+$|\p{L})/u,
    message: "must be a number or contain a letter"
  )
end

defp mathematical_validation(changeset) do
  revenue = get_field(changeset, :revenue)
  expense = get_field(changeset, :expense)
  net_gain = get_field(changeset, :net_gain)

  with {:is_valid, true} <- {:is_valid, changeset.valid?},
       {:math_validation, true} <-
         {:math_validation, Decimal.sub(revenue, expense) == Decimal.new(net_gain)} do
    changeset
  else
    {:is_valid, false} ->
      changeset

    {:math_validation, false} ->
      add_error(changeset, :net_gain, "must equal revenue minus expense")
  end
end