add revisions

db/migrate/20260506121640_create_template_versions.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class CreateTemplateVersions < ActiveRecord::Migration[8.1]
+  def change
+    create_table :template_versions do |t|
+      t.references :template, null: false, foreign_key: true, index: false
+      t.references :account, null: false, foreign_key: true, index: true
+      t.references :author, null: false, foreign_key: { to_table: :users }, index: true
+      t.text :data, null: false
+      t.string :sha1, null: false
+      t.timestamps
+    end
+
+    add_index :template_versions, %i[template_id sha1], unique: true
+  end
+end