custom validation without model in rails

I have created following class just to have validation and custom validation for parameters for my ajax message:

class Message
  include ActiveModel::Validations
  include ActiveModel::Conversion  
  extend ActiveModel::Naming  

  attr_accessor :attributes

  validates_inclusion_of :temp_inside, :in => 0..30
  validates_inclusion_of :temp_outside, :in => -50..20
  validates_presence_of :isol
  validates_inclusion_of :height, :length, :width, :in => 1..500
  validate :temp_outside_cannot_be_greater_than_temp_inside 

  def temp_outside_cannot_be_开发者_Python百科greater_than_temp_inside  
     errors.add(:temp_outside, "can't be greater than total value") if
        temp_outside > temp_inside
  end

  def initialize(attributes = {})
    @attributes = attributes 
  end

  def read_attribute_for_validation(key)
    @attributes[key]
  end

  def persisted?  
    false  
  end
end

and getting following error inside "temp_outside_cannot_be_greater_than_temp_inside"

NoMethodError (undefined method `>' for :temp_outside:Symbol):

any idea?

You need to check the value of temp_outside, as it seems to be a symbol in this case, not a number