Ecto:如何在更新中调用函数

defmodule MyApp.User do
  use Ecto.Schema

  schema "users" do
    field :name, :string
    field :age, :integer
  end

  def changeset(user, attrs) do
    user
    |> cast(attrs, [:name, :age])
    |> validate_required([:name, :age])
    |> update_age
  end

  defp update_age(changeset) do
    case get_field(changeset, :age) do
      nil -> changeset
      age ->
        updated_age = age + 1
        put_change(changeset, :age, updated_age)
    end
  end
end