Updated migration generator template.

generators/paperclip/templates/paperclip_migration.rb.erb

 class <%= migration_name %> < ActiveRecord::Migration
-  def self.up
+  def change
 <% attachments.each do |attachment| -%>
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_name, :string
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_content_type, :string
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_size, :integer
     add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_updated_at, :datetime
-<% end -%>
-  end
-
-  def self.down
-<% attachments.each do |attachment| -%>
-    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_name
-    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_content_type
-    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_file_size
-    remove_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_updated_at
+    add_column :<%= class_name.underscore.camelize.tableize %>, :<%= attachment %>_fingerprint, :string, length: 32
 <% end -%>
   end
 end