wiki/priv/repo/migrations/20200801233918_create_page_links.exs

defmodule Wiki.Repo.Migrations.CreatePageLinks do
  use Ecto.Migration

  def change do
    create table(:page_links) do
      add :from_id, references(:pages, on_delete: :delete_all), primary_key: true
      add :to_id, references(:pages, on_delete: :delete_all), primary_key: true
    end

    create index(:page_links, [:from_id])
    create index(:page_links, [:to_id])

    create unique_index(:page_links, [:from_id, :to_id],
             name: :page_link_from_id_to_id_unique_index
           )
  end
end