Trial example URL generation

Trial.rb

class Trial < ActiveRecord::Base

	TRIAL_TYPES = ["usability","clickmap","interview","survey"]

	has_many :stints, :dependent => :nullify
  has_many :tasks, :dependent => :destroy
	before_validation :generate_access_token
  attr_accessible :url, :access_token, :trial_type, :title, :description

  validates_presence_of :access_token, :trial_type, :title, :description
  validates_uniqueness_of :access_token

  accepts_nested_attributes_for :tasks

  protected
  def generate_access_token
  	self.access_token = rand(36**8).to_s(36) if self.new_record? and self.access_token.nil?
  end
end