settings.ex

defmodule App.Models.Settings do
  defstruct [
    newsletter:          false,
    publish_profile:     true,
    email_notifications: true
  ]

  defmodule Type do
    @behaviour Ecto.Type
    alias App.Models.Settings

    def type, do: :json

    def cast(%Settings{} = settings), do: {:ok, settings}
    def cast(%{} = settings),         do: {:ok, struct(Settings, settings)}
    def cast(_other),                 do: :error

    def load(value), do: Poison.decode(value, as: App.Models.Settings)
    
    def dump(value), do: Poison.encode(value)
  end
end

# and here is the jsonb version
#
defmodule App.Models.Settings do
  defstruct [
    newsletter:          false,
    publish_profile:     true,
    email_notifications: true
  ]

  defmodule Type do
    @behaviour Ecto.Type
    alias App.Models.Settings

    # ***** Change this line *****
    def type, do: :jsonb

    def cast(%Settings{} = settings), do: {:ok, settings}
    def cast(%{} = settings),         do: {:ok, struct(Settings, settings)}
    def cast(_other),                 do: :error

    def load(value), do: Poison.decode(value, as: App.Models.Settings)

    # ***** Change this line *****
    def dump(value), do: {:ok, value}
  end
end