add paper trail

db/migrate/20210817233439_create_versions.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+# This migration creates the `versions` table, the only schema PT requires.
+# All other migrations PT provides are optional.
+class CreateVersions < ActiveRecord::Migration[6.1]
+  # The largest text column available in all supported RDBMS is
+  # 1024^3 - 1 bytes, roughly one gibibyte.  We specify a size
+  # so that MySQL will use `longtext` instead of `text`.  Otherwise,
+  # when serializing very large objects, `text` might not be big enough.
+  TEXT_BYTES = 1_073_741_823
+
+  def change
+    create_table(:versions) do |t|
+      t.string(:item_type, { null: false })
+      t.bigint(:item_id,   null: false)
+      t.string(:event,     null: false)
+      t.string(:whodunnit)
+      t.text(:object, limit: TEXT_BYTES)
+
+      t.datetime(:created_at)
+    end
+    add_index(:versions, [:item_type, :item_id])
+  end
+end