View
=====
    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: changeset[:errors]}
    end

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} ->
           json(conn, changeset)
      end
  end


Registration.create
====
    def create(changeset, repo) do
      changeset
      |> put_change(:password, hashed_password(changeset.params["plain_password"]))
      |> repo.insert()
    end