Rails - Mar 2006 - unused composed_of bits

I implemented a Temperature model for my application.  It is pretty basic, 
composed of a temperature, a unit and some conversion methods.  In my app model 
I decided to store temperature values in Fahrenheit, so there is no need to 
remember the units between invocations.  I am having a little trouble composing 
my app model.

A little bit of my temperature class:

class Temperature
# Composed of a float with 1 sig fig and units of Celsius, Fahrenheit or Kelvin
# Implements to_s, to_html and a number of conversions and bang conversions

attr_reader :temp, :units

def initialize( temperature, units = "F" )
   unless valid_units?(units)
     units = "F"
   end
   @temp = temperature = ((10 * temperature).to_f.round)/10.0
   @units = units.upcase
end

def to_c
   convert_to("C")
end
... etc.

So in my app model:

class Profile < ActiveRecord::Base
   composed_of :temperature, :class_name => Temperature,
               :mapping => [ :temp, :temp ]

   def before_save
     self.temperature.to_f!
   end

The table corresponding to Profile has a column named temp.  What happens to 
the units?  Is it merely ignored?

When I navigate to /profiles/new I get:

undefined method `temperature.temp'' for #<Profile:0xb7395660>

Extracted source (around line #10):

7:   </div>
8:   <div class="form-element">
9:     <label
for="profile_temperature">Temperature</label>
10:     <%= text_field ''profile'',
''temperature.temp'' -%>&deg;<br />

Controller:
def new
   @profile = Profile.new
   @profile.temperature = Temperature.new(0)
   render :layout => !request.xhr?
end

How do I create a text_field for just the temp part of the Temperature object? 
  Or should I just cut to the chase and do a <%= text_field
''profile'', ''temp''
%> and create the Temperature object in the controller?

Regards,
--Dean - Unscrambler of eggs
--
Take your time, take your chances
[3278.7 km, 273.4] Apparent Rennerian
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