packed_fields

ActiveRecord::Schema.define(:version => 1) do
  create_table :mixins do |t|
    t.column :packed, :text
  end
end

class Mixin < ActiveRecord::Base
  packed :fields => [:foo, :bar]
end

m = Mixins.new
m.foo = 'blah'
m.save #=> #<Mixin id: 1, packed: {:foo=>"blah"}>