Some Weird Weird Ruby (or nest Classes and Inheritence)

Thinking cap time. I am working on a CMS and the short of it is that a Page will have many PageBlock objects. The PageBlock is versioned and can have multiple things associated with it (i.e. Links or Files or Other Stuff, thankfully each page block is homogenous). I decided that the Links/Files will be serialized. So I wrote a serializing helper object. This serializing object

class PageBlock < ActiveRecord::Base
  class << self
    # I want to be able to configure the underlying DataSerializer
    # in the containing class
    delegate :set_valid_serialized_keys, :to => :data_serializing_class
    def data_serializing_class
      self::DataSerializer
    end
  end
  class DataSerializer
    class << self
      def set_valid_serialized_keys( *attrs )
        write_inheritable_attribute :valid_serialized_keys, attrs
        class_inheritable_reader    :valid_serialized_keys
      end
    end
    
    def add_data(data = {})
      data.assert_valid_keys(valid_serialized_keys)
      ... do the magic ...
    end
  end
end

Now

$ PageBlock.valid_serialized_keys
=> NoMethodError: undefined method `valid_serialized_keys' for PageBlock::DataSerializer:Class

class PageLinkBlock < PageBlock
  set_valid_serialized_keys :path, :name
end

$ PageBlock.valid_serialized_keys
=> [:path, :name]

DOH!!! Man that is definitely not the behavior I want. I guess my nested Class has some behavior that I'm not aware of. I'm certain the behavior is intentional, I just didn't know about it

So the solution?

class PageBlock < ActiveRecord::Base
  class << self
    # I want to be able to configure the underlying DataSerializer
    # in the containing class
    delegate :set_valid_serialized_keys, :to => :data_serializing_class

    def data_serializing_class
      self::DataSerializer
    end

    def inherited(page_block_subclass)
      page_block_subclass.module_eval <<-EOV
      class DataSerializer < PageBlock::DataSerializer
      end
      EOV
      super
    end

  end
  class DataSerializer
    class << self
      def set_valid_serialized_keys( *attrs )
        write_inheritable_attribute :valid_serialized_keys, attrs
        class_inheritable_reader    :valid_serialized_keys
      end
    end
    
    def add_data(data = {})
      data.assert_valid_keys(valid_serialized_keys)
      ... do the magic ...
    end
  end
end

Then I define PageLinkBlock and

$ PageBlock.valid_serialized_keys
=> NoMethodError: undefined method `valid_serialized_keys' for PageBlock::DataSerializer:Class

Alas, the behavior that I want. Time to dig out the Pickaxe Book to see if there is a reference to this.