dontdothis.rb

class UsersController < ApplicationController
...
def create
    referral_id = User.find_valid_referral(params[:user][:referral])
    @user = User.new(params[:user].merge(:referral_id => referral_id))
    ...
  end
...
end

class User < ActiveRecord::Base
...
  def self.find_valid_referral(username)
    user = User.find_by_username(username)
    if user.nil?
      return 999999999999999999
    else
      return user.id
    end
  end
...
end