Use migration classes in migrations where current definition conflicts with older (#26390)

db/migrate/20170105224407_add_shortcode_to_media_attachments.rb

@@ -1,12 +1,19 @@
 # frozen_string_literal: true
 
 class AddShortcodeToMediaAttachments < ActiveRecord::Migration[5.0]
+  class MigrationMediaAttachment < ApplicationRecord
+    self.table_name = :media_attachments
+    scope :local, -> { where(remote_url: '') }
+  end
+
   def up
     add_column :media_attachments, :shortcode, :string, null: true, default: nil
     add_index :media_attachments, :shortcode, unique: true
 
+    MigrationMediaAttachment.reset_column_information
+
     # Migrate old links
-    MediaAttachment.local.update_all('shortcode = id')
+    MigrationMediaAttachment.local.update_all('shortcode = id')
   end
 
   def down