add folders migration

db/migrate/20230920202947_add_folder_id_to_templates.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+class AddFolderIdToTemplates < ActiveRecord::Migration[7.0]
+  class MigrationTemplateFolder < ApplicationRecord
+    self.table_name = 'template_folders'
+  end
+
+  class MigrationAccount < ApplicationRecord
+    self.table_name = 'accounts'
+  end
+
+  class MigrationTemplate < ApplicationRecord
+    self.table_name = 'templates'
+  end
+
+  class MigrationUser < ApplicationRecord
+    self.table_name = 'users'
+  end
+
+  def up
+    add_reference :templates, :folder, foreign_key: { to_table: :template_folders }, index: true, null: true
+
+    MigrationAccount.all.pluck(:id).each do |account_id|
+      author_id = MigrationUser.where(account_id:).minimum(:id)
+
+      next if author_id.blank?
+
+      folder = MigrationTemplateFolder.create_with(author_id:)
+                                      .find_or_create_by(name: 'Default', account_id:)
+
+      MigrationTemplate.where(account_id:).update_all(folder_id: folder.id)
+    end
+
+    change_column_null :templates, :folder_id, false
+  end
+
+  def down
+    remove_column :templates, :folder_id
+  end
+end