ash_hq/priv/repo/migrations/20220823191104_add_library_order.exs

defmodule AshHq.Repo.Migrations.AddLibraryOrder do
  @moduledoc """
  Updates resources based on their most recent snapshots.

  This file was autogenerated with `mix ash_postgres.generate_migrations`
  """

  use Ecto.Migration

  def up do
    alter table(:libraries) do
      add(:order, :bigint, null: true)
    end

    execute("""
    WITH sorted AS (SELECT id, ROW_NUMBER() OVER(ORDER BY name ASC) AS new_order FROM libraries)
    UPDATE libraries SET "order" = (SELECT new_order FROM sorted WHERE sorted.id = libraries.id) - 1;
    """)

    alter table(:libraries) do
      modify(:order, :bigint, null: false)
    end
  end

  def down do
    alter table(:libraries) do
      remove(:order)
    end
  end
end