gistfile1.rb

class Order
      has_many :order_order_properties, :dependent => :destroy,
                                        :attributes => true
      has_many(:properties, :class_name => "OrderProperty",
                            :through => :order_order_properties,
                            :source => :order_property) 


      named_scope :with_property_value, lambda { |property_name, value|
        {
          :include => [:properties, :order_order_properties],
          :conditions => ['order_properties.name = ? AND order_order_properties.value = ?', property_name, value]
        }
      }
...
end

# orders = Order.with_property_value("order_motion_order_id", order_number)