def create
    @advertiser = Advertiser.new
    @user = User.new
    attrs = params[:advertiser]

    unless (u = params[:user]).blank?
      u.merge!({:user_type => UserType["Advertiser"]})
      @user = User.create(u)
      if @user.valid?
        @advertiser.user_id = @user.id
        #raise @advertiser.inspect
      end
    end

    ...

end

class User < ActiveRecord::Base

  belongs_to :user_type
  belongs_to :call_center_company

  has_many :lead_histories
  has_many :advertisers

  validates_presence_of :username
  validates_presence_of :password

end