```ruby
class ChangeAttachmentDirName < ActiveRecord::Migration
  def up
    ActiveRecord::Base.connection.execute("UPDATE paperclipdb SET dir_name='/paperclipdb'+dir_name")
  end

  def down
    ActiveRecord::Base.connection.execute("UPDATE paperclipdb SET dir_name=REPLACE(dir_name, '/paperclipdb', '')")
  end
end
```

Add correct migration to update routes in db
user
```ruby
class ChangeAttachmentDirName < ActiveRecord::Migration
  def up
    Paperclipdb::Attachment.all.each{|a| a.update_attribute(:dir_name, "/paperclipdb#{a.dir_name}") unless a.dir_name.start_with?("/paperclipdb")}
  end

  def down
    Paperclipdb::Attachment.all.each{|a| a.update_attribute(:dir_name, a.dir_name.gsub("/paperclipdb/", "/")) if a.dir_name.start_with?("/paperclipdb")}
  end
end
```
assistant