File is the Ruby representation of the file class. It is a Very Bad Idea to reuse that name as is. Reusing names defined in Ruby stdlib classes is a bad idea.

File is the Ruby representation of the file class. It is a Very Bad Idea to reuse that name as is. Reusing names defined in Ruby stdlib classes is a bad idea. Name the model after what the file is used for, eg LockFile. Another option if you absolutely have to use that name, wrap it in a module, eg module Foo class File < ActiveRecord::Base end end And then always refer to it with the module prefix, ie Foo::File.