ActiveRecord#becomes doesn't destroy associations any more

gistfile1.rb

# Normally if you do
class A < ActiveRecord::Base
  belongs_to :c
end

class B < A
end

b = B.new
b.c = C.new
a = b.becomes(A)

# you find that 

a.c == nil

# to fix that, we have an initializer:

class ActiveRecord::Base

  def becomes_with_association_cache(klass)
    became = becomes_without_association_cache(klass)
    became.instance_variable_set("@association_cache", @association_cache)
    became
  end
  alias_method_chain :becomes, :association_cache

end