Controller
====
  def register(conn, %{"email" => email, "login" => login, "password" => password} = params) do
    changeset = App.User.changeset(%App.User{}, %{email: email, login: login, plain_password: password})
      case Registration.create(changeset, App.Repo) do
        {:ok, changeset} ->
           render conn, "register.json", user: %App.User{email: email, login: login}
        {:error, changeset} ->
           render(conn, App.ChangesetView, "error.json", changeset: changeset)
      end
  end

View
====
defmodule App.ChangesetView do
  use App.Web, :view

  @doc """
  Traverses and translates changeset errors.
  See `Ecto.Changeset.traverse_errors/2` and
  `ApiTest.ErrorHelpers.translate_error/1` for more details.
  """
  def translate_errors(changeset) do
    Ecto.Changeset.traverse_errors(changeset, &translate_error/1)
  end

  def render("error.json", %{changeset: changeset}) do
    # When encoded, the changeset returns its errors
    # as a JSON object. So we just pass it forward.
    %{errors: translate_errors(changeset)}
  end
end