Track dirty for not-persisted attribute in an ActiveRecord object in rails

Question

I have an object that inherits from ActiveRecord, yet it has an attribute that is not persisted in the DB, like:

 class Foo < ActiveRecord::Base
   attr_acces         


        

Answer 1

I figured out a solution that worked for me...

Save this file as lib/active_record/nonpersisted_attribute_methods.rb: https://gist.github.com/4600209

Then you can do something like this:

require 'active_record/nonpersisted_attribute_methods'
class Foo < ActiveRecord::Base
  include ActiveRecord::NonPersistedAttributeMethods
  define_nonpersisted_attribute_methods [:bar]
end

foo = Foo.new
foo.bar = 3
foo.bar_changed? # => true
foo.bar_was # => nil
foo.bar_change # => [nil, 3]
foo.changes[:bar] # => [nil, 3]

However, it looks like we get a warning when we do it this way:

DEPRECATION WARNING: You're trying to create an attribute `bar'. Writing arbitrary attributes on a model is deprecated. Please just use `attr_writer` etc.

So I don't know if this approach will break or be harder in Rails 4...