Just in case anyone is looking for a way to use postgres enum types with ecto, here’s how (without any additional dependencies).

defmodule Invoice.Status do
  @moduledoc """
  The status of payment; whether the invoice has been paid or not.

  Enumeration members:
  - `:payment_automatically_applied`
  - `:payment_complete`
  - `:payment_declined`
  - `:payment_due`
  - `:payment_past_due`
  """

  @behaviour Ecto.Type

  statuses = [
    :payment_automatically_applied,
    :payment_complete,
    :payment_declined,
    :payment_due,
    :payment_past_due
  ] |> Enum.map(fn status ->
    {status, to_string(status)}
  end)

  @doc "Returns the underlying schema type for the custom type"
  @spec type :: :invoice_status
  def type, do: :invoice_status

  @doc "Casts the given input to the custom type"
  @spec cast(atom | binary) :: {:ok, atom} | :error
  def cast(status)

  for {atom, string} <- statuses do
    def cast(unquote(atom)), do: {:ok, unquote(atom)}
    def cast(unquote(string)), do: {:ok, unquote(atom)}
  end

  def cast(_other), do: :error

  @doc "Loads the given term into a custom type"
  @spec load(binary) :: {:ok, atom}
  def load(status)

  for {atom, string} <- statuses do
    def load(unquote(string)), do: {:ok, unquote(atom)}
  end

  @doc "Dumps the given term into an Ecto native type"
  @spec dump(atom | binary) :: {:ok, binary} | :error
  def dump(status)

  for {atom, string} <- statuses do
    def dump(unquote(atom)), do: {:ok, unquote(string)}
    def dump(unquote(string)), do: {:ok, unquote(string)}
  end

  def dump(_other), do: :error
end

No doubt you could write your own code to create a custom Ecto type. The point of this small and focused library is to do the metaprogramming for you so don’t need to write that code every time you need to create an Enum in Ecto. With EctoEnum, you just need to write a few lines of code to have a StatusEnum, DayOfWeekEnum, etc… Also, this library actually has tests and is used by many other devs. That’s the point of having libraries and sharing packages, so we can focus on other work.

Oh and EctoEnum works with Postgres’s Enum type or a plain ol’ integer. It will have support for MySQL’s Enum type in the future too.