Using the after_save callback to modify the same object without triggering the callback again (recursion)

def your_after_save_func
  YourModel.without_callbacks(:your_after_save_func) do
    Your updates/changes
  end
end

send(name.to_s + '=', value)

def before_save
  @attempted_save_level ||= 0
  @attempted_save_level += 1
end

def after_save
  if (@attempted_save_level == 1)
     #fill in logic here

     save  #fires before_save, incrementing save_level to 2, then after_save, which returns without taking action

     #fill in logic here

  end
  @attempted_save_level -= 1  # reset the "prevent infinite recursion" flag
end

Class Foo << ActiveRecord::Base
    after_save :init_bar_attr, :if => "bar_attr.nil?"    # just make sure this is false after the callback runs

    def init_bar_attr
        self.bar_attr = "my id is: #{self.id}"

        # careful now, let's save only if we're sure the triggering condition will fail
        self.save if bar_attr
    end