for https://github.com/willbryant/columns_on_demand/issues/2

monkey_patch_columns_on_demand_4_2_0_for_rails_4_2_1.rb

# monkey patch for https://github.com/willbryant/columns_on_demand/issues/2

require 'active_record'
require 'columns_on_demand'


module ColumnsOnDemand
  module BaseMethods

    # COPIED
    def columns_on_demand(*columns_to_load_on_demand)
      class_attribute :columns_to_load_on_demand, :instance_writer => false
      self.columns_to_load_on_demand = columns_to_load_on_demand.empty? ? blob_and_text_columns : columns_to_load_on_demand.collect(&:to_s)

      extend ClassMethods
      include InstanceMethods

      class <<self
        unless ActiveRecord::VERSION::MAJOR > 3 ||
          (ActiveRecord.const_defined?(:AttributeMethods) &&
            ActiveRecord::AttributeMethods::const_defined?(:Serialization) &&
            ActiveRecord::AttributeMethods::Serialization::const_defined?(:Attribute))
          alias_method_chain :define_read_method_for_serialized_attribute, :columns_on_demand
        end
        alias_method_chain :reset_column_information,        :columns_on_demand
      end
      alias_method_chain   :attributes,                      :columns_on_demand
      alias_method_chain   :attribute_names,                 :columns_on_demand
      alias_method_chain   :read_attribute,                  :columns_on_demand
      alias_method_chain   :read_attribute_before_type_cast, :columns_on_demand
      alias_method_chain   :missing_attribute,               :columns_on_demand
      alias_method_chain   :reload,                          :columns_on_demand
      # CHANGED = FROM HERE
      alias_method_chain   :attribute_changed_in_place?,     :columns_on_demand if ActiveRecord::AttributeMethods::Dirty.instance_methods.include?(:changed_attributes)
      alias_method_chain   :_read_attribute,                 :columns_on_demand
      # CHANGED = TO HERE
    end

  end
end


module ColumnsOnDemand
  module InstanceMethods

    def attribute_changed_in_place_with_columns_on_demand?(attr_name)
      column_loaded?(attr_name) && attribute_changed_in_place_without_columns_on_demand?(attr_name)
    end

    def _read_attribute_with_columns_on_demand(attr_name, &block)
      ensure_loaded(attr_name)
      _read_attribute_without_columns_on_demand(attr_name, &block)
    end

  end
end


class ActiveRecord::Relation

  # override build_select already chained to build_select_with_columns_on_demand
  private \
  def build_select(arel)
    if select_values.any?
      arel.project(*arel_columns(select_values.uniq))
    else
      if klass < ColumnsOnDemand::InstanceMethods
        selects = [default_select(true)]
        expanded_select = selects.map do |field|
          if (Symbol === field || String === field) && columns_hash.key?(field.to_s)
            arel_table[field]
          else
            field
          end
        end
        arel.project(*expanded_select)
      else
        arel.project(@klass.arel_table[Arel.star])
      end
    end
  end

end