add migration of files from carrierwave to activestorage

Author: kkoehn

db/migrate/20250907210200_migrate_carrierwave_files_to_active_storage.rb

@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+class MigrateCarrierwaveFilesToActiveStorage < ActiveRecord::Migration[8.0]
+  disable_ddl_transaction!
+
+  module CodeOcean
+    class File < ActiveRecord::Base
+      self.table_name = 'files'
+
+      # Manually set class name to avoid problems with ActiveStorage's polymorphic association
+      def self.name = 'CodeOcean::File'
+
+      has_one_attached :attachment
+    end
+  end
+
+  def up
+    say_with_time 'Migrating CarrierWave files to ActiveStorage' do
+      migrated = 0
+      skipped_existing = 0
+      missing = 0
+
+      scope = CodeOcean::File.unscoped.where.not(native_file: [nil, ''])
+      total = scope.count
+
+      scope.find_in_batches(batch_size: 1000).with_index do |batch, i|
+        say "Processing batch ##{i + 1} (#{[(i * 1000) + 1, total].min}-#{[(i + 1) * 1000, total].min} of #{total})", true
+        batch.each do |record|
+          if record.attachment.attached?
+            skipped_existing += 1
+            next
+          end
+
+          filename = record[:native_file]
+          next if filename.blank?
+
+          old_path = Rails.public_path.join('uploads', 'files', record.id.to_s, filename)
+
+          unless ::File.exist?(old_path)
+            missing += 1
+            next
+          end
+
+          begin
+            File.open(old_path, 'rb') do |io|
+              record.attachment.attach(io:, filename: filename)
+            end
+            migrated += 1
+          rescue StandardError => e
+            warn "Failed to attach file for files.id=#{record.id}: #{e.class}: #{e.message}"
+          end
+        end
+      end
+
+      say "Done. Migrated: #{migrated}, already attached: #{skipped_existing}, missing source files: #{missing}", true
+
+      migrated
+    end
+  end
+
+  def down
+    say 'No rollback for CarrierWave -> ActiveStorage file migration.'
+  end
+end

db/migrate/20250907230600_remove_native_file_from_files.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class RemoveNativeFileFromFiles < ActiveRecord::Migration[8.0]
+  def up
+    if column_exists?(:files, :native_file)
+      remove_column :files, :native_file, :string
+    end
+  end
+
+  def down
+    unless column_exists?(:files, :native_file)
+      add_column :files, :native_file, :string
+    end
+  end
+end