gistfile1.rb

class Position < ActiveRecord::Base
  attr_protected :account_id, :created_at, :updated_at
  
  belongs_to :account
  
  #### Option 1 ####
  attr_restricted :job_id
  
  # assigns attribute if this method returns true
  def allow_job_id_assignment?(id)
    account.jobs.find_by_id(id) if account
  end

  #### Option 2: with a block ####
  attr_restricted :job_id do |id|
    account.jobs.find_by_id(id) if account
  end
end