medium post

registration_controller.ex

defmodule App.RegistrationController do
  use App.Web, :controller
  alias App.{Registration, Repo}

  def new(conn, _params) do
    changeset = Registration.changeset(%Registration{})
    render conn, :new, changeset: changeset
  end

  def create(conn, %{"registration" => registration_params}) do
    case Registration.handle_registration(registration_params) do
      {:ok, _} ->
        redirect conn, to: registration_path(conn, :new)
      {:error, _operation, error_changeset, _changes} ->
        changeset = 
          Registration.changeset(%Registration{})
          |> copy_errors(error_changeset)
        render conn, :new, changeset: %{changeset | action: :insert}
    end
  end

  defp copy_errors(to, from) do
    Enum.reduce from.errors, to, fn {field, {msg, additional}}, acc ->
      Ecto.Changeset.add_error(acc, field, msg, additional: additional)
    end
  end
end