gistfile1.rb

class User < ActiveRecord:Base
    ROLE_TYPES = %W[Company Developer]

    validates_presence_of :email, :allow_blank => false, :allow_nil => false
    validates_uniqueness_of :email
    validates_email_format_of :email

    attr_accessible :email
end

class Developer < ActiveRecord::Base
    acts_as_role

    validates_numericality_of :phone_number, :allow_blank => true

    attr_accessible :phone_number
end

class ApplicationController < ActionController::Base
    def index
        @user = Developer.new
    end
end

= simple_form_for @user, :validate => true do |f|
    =f.input :email, :required => true
    =f.input :phone_number, :required => true

# In this example, only phone_number will be validated