module ActiveRecord
  module CheckArrayBeforeUpdate
    def mark_arrays_for_update
      @attributes_cache.each do |name, value|
        attribute_will_change!(name) if Array === value && _read_attribute(name) != value
      end
    end
  end

  module CheckArrayBeforeUpdate
    def self.included(base)
      base.alias_method_chain :update, :check_array
      base.send(:alias_method, :_read_attribute, :read_attribute)
    end

    def update_with_check_array
      mark_arrays_for_update
      update_without_check_array
    end
  end
  Base.__send__ :include, CheckArrayBeforeUpdate
end