audit.rb

before_update :audit

  def audit 
    if self.changed?
      # find columns we want to audit
      audit_columns = UserAudit.column_names.reject{|c| %w{id created_at updated_at}.include?(c)}
      # add the user_id
      data = self.attributes.dup.merge('user_id' => self.id)
      # copy the pre-modified values
      self.changes.each {|att, a| data[att] = a[0]}
      # only keep the columns we columns we care about
      data.keep_if{|c, v| audit_columns.include?(c)}
      # save data
      UserAudit.create!(data)
    end
  end