aaaa.rb

require 'yaml'
#require 'mongoid'

class Bump
  attr_reader :data
  
  def initialize
    @data = [1,2,3,4,5]
  end
end

class Doc
  attr_accessor :id
  
  def initialize
    @id = Bump.new
  end
end

a = Doc.new

puts "\n\nWRONG:"
puts a.to_yaml

class << a.id.data
  def to_yaml_style; :inline; end
end

puts "\n\nRIGHT:"
puts a.to_yaml