The database changes dandelion needs, called from your own migration — the way Oban.Migration is:

defmodule MyApp.Repo.Migrations.AddDandelion do
  use Ecto.Migration

  def up, do: Dandelion.Migration.up()
  def down, do: Dandelion.Migration.down()
end

Run it after the Oban migration: it adds an index to oban_jobs for Dandelion.Queue.Ordered.