model.ex

defmodule ElixirStream.Entry do  
  use ElixirStream.Web, :model
  use Ecto.Model.Callbacks
  alias ElixirStream.User

  before_insert :set_slug

  schema "entries" do
    field :email, :string
    field :author_name, :string
    field :title, :string
    field :body, :string
    field :slug, :string
    belongs_to :user, User
    timestamps
  end

  @optional_fields ~w(email author_name)
  @required_fields ~w(title body)

  def changeset(model, params \\ :empty) do
    model
    |> cast(params, @required_fields, @optional_fields)
    |> validate_length(:title, min: 5)
    |> validate_length(:body, min: 15)
    |> validate_length(:body, max: 500)
  end

  def set_slug(changeset) do
    slug = Ecto.Changeset.get_field(changeset, :title) |>
    String.strip |> String.downcase |> String.replace(~r/([^a-z0-9])+/, "-")
    change(changeset, %{slug: slug})
  end
end