#blog_snippets

week_may4_validation06.ex

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

  with true <- revenue != nil,
       true <- expense != nil,
       true <- net_gain != nil,
       true <- Decimal.sub(revenue, expense) == Decimal.new(net_gain) do
    changeset
  else
    _ -> add_error(changeset, :net_gain, "must equal revenue minus expense")
  end
end