neiam /gitgud

defmodule GitGud.Repo.Migrations.CreateRepositoryRoots do
  use Ecto.Migration

  # A repo's parentless commits are its lineage fingerprint. Two repos
  # sharing one are forks of each other however the copy was made — so
  # this finds forks whose `parent_repository_id` link was never set
  # (imports) or was severed.
  def change do
    create table(:repository_roots) do
      add :repository_id, references(:repositories, on_delete: :delete_all), null: false
      add :sha, :binary, null: false

      timestamps(type: :utc_datetime, updated_at: false)
    end

    create unique_index(:repository_roots, [:repository_id, :sha])
    # The lookup that matters: "who else shares this root?"
    create index(:repository_roots, [:sha])
  end
end