Behaviour for an ArcadeDB migration — a versioned pair of forward/backward steps. Migrations are tenant-blind schema changes; author raw DDL/DML via Arcadic.command/4 in up/1 and down/1.

Only :ok finalizes a migration (Arcadic.Migrator marks it done); an {:error, reason} return (or a raise) leaves the attempt's marker in place and the next migrator run refuses until you reconcile — see Arcadic.Migrator's "Crash recovery" docs.

Migrations SHOULD be idempotent (IF NOT EXISTS / IF EXISTS) — replay can still happen outside the marker window (a manually deleted tracking row, a version number reused) — but the marker, not author discipline, is the crash-safety mechanism.

defmodule MyApp.Migrations.V1 do
  @behaviour Arcadic.Migration
  @impl true
  def version, do: 1
  @impl true
  def up(conn) do
    Arcadic.command!(conn, "CREATE VERTEX TYPE User IF NOT EXISTS", %{}, language: "sql")
    :ok
  end
  @impl true
  def down(conn) do
    Arcadic.command!(conn, "DROP TYPE User IF EXISTS", %{}, language: "sql")
    :ok
  end
end