ActiveRecord serialization throws SerializationTypeMismatch if I try to serialize a AR object

I am not able to reproduce this problem in Rails edge.

class Brake < ActiveRecord::Base

  serialize :car, Car

end

ree-1.8.7-2010.02 > Car.create! :name => 'honda'
   (0.2ms)   SELECT name
 FROM sqlite_master
 WHERE type = 'table' AND NOT name = 'sqlite_sequence'

  AREL (0.3ms)  INSERT INTO "cars" ("name") VALUES ('honda')
 => #<Car id: 1, name: "honda"> 
ree-1.8.7-2010.02 > Brake.create! :car => Car.last
  Car Load (0.3ms)  SELECT "cars".* FROM "cars" ORDER BY cars.id DESC LIMIT 1
  AREL (0.5ms)  INSERT INTO "brakes" ("car") VALUES ('--- !ruby/object:Car 
attributes: 
 name: honda
 id: 1
attributes_cache: {}

changed_attributes: {}

destroyed: false
marked_for_destruction: false
new_record: false
previously_changed: {}

readonly: false
')
 => #<Brake id: 1, car: #<Car id: 1, name: "honda">> 
ree-1.8.7-2010.02 > Brake.last
  Brake Load (0.4ms)  SELECT "brakes".* FROM "brakes" ORDER BY brakes.id DESC LIMIT 1
 => #<Brake id: 1, car: #<Car id: 1, name: "honda">> 
ree-1.8.7-2010.02 >

A workaround for Rails 3.0.3:

I spent a while scanning through commit between July 28 and December 4 and could not find a patch that atomically fixed this.

If you need to stay on the stable brach for the time being, this can serve as a workaround. Change this:

  def []=(key, value)
    @keys << key unless has_key?(key)
    super
  end

to this:

  def []=(key, value)
    (@keys||=[]) << key unless has_key?(key)
    super
  end

in active_support/ordered_hash.rb. I know it's kind of ugly, but it's the smallest change that resolves the issue.