Rails - Sep 2005 - model constructor errors.

I have a model; I do photo = Photo.new(parameters) parameters
contains:
{"picture"=>#<File:C:/DOCUME~1/BART~1/LOCALS~1/Temp/CGI3180.1>}
so i expect that the def picture=(filename) method is called in this
constructor.. this is not the case. Does anyone know why?


      params[:photo].each_pair do |id, parameters|

          photo = Photo.new(parameters)
     end


class Photo < ActiveRecord::Base
  attr_accessor :file, :content_type, :size, :extension, :local_path, :destroyed
  attr_reader :original_filename
  attr_accessible :title, :description

  has_many :comments, :exclusively_dependent => true
  belongs_to :user
  
  validates_presence_of :title
  validates_presence_of :description, :on => :update
 
  acts_as_taggable

  def picture=(picture_field)
    logger.debug "in picture method" ## DEBUGGING
    @local_path = picture_field.local_path
    @filename = base_part_of(picture_field.original_filename)
    @extension = @filename.split(''.'').pop
    if @extension == "jpeg" 
      @extension = "jpg" ## convention
    end
    @content_type = picture_field.content_type.chomp
    @size = picture_field.size
    
    picture_field.rewind
    @file = picture_field.read  

    self.title = @filename
  end

  ..
end