message.rb

class Message < ActiveRecord::Base
  belongs_to :sender, :class_name => "User"
  belongs_to :receiver, :class_name => "User"

  validates_presence_of :body

  before_validation_on_create :set_read

  def set_read
    self.read = false
  end

  def not(who)
    if self.sender != who
      self.sender
    else
      self.receiver
    end
  end
end