prefix_id.ex

defmodule PrefixID do

  @doc """
  Custom Ecto.Type use macro

  Example:

      use PrefixID, prefix: "secret_key"

  After this, the Ecto type will have
  all features defined below.
  """
  defmacro __using__(opts) do
    prefix = opts[:prefix] || "test"

    quote bind_quoted: [prefix: prefix] do
      @behaviour Ecto.Type

      def type, do: :string

      def cast(string) when is_binary(string) do
        {:ok, string}
      end

      defp prepared_prefix do
        unquote(prefix) <> "_"
      end

      def autogenerate() do
        prepared_prefix() <> Random.base58()
      end

      def cast(_), do: :error

      def dump(string) when is_binary(string) do
        {:ok, string}
      end

      def load(string) when is_binary(string) do
        {:ok, string}
      end
    end
  end
end