ror:activescaffold:如何使更新列fetaure成为条件?

Schema:

action_types
------------
id
name
description

actions
-------
id
action_type_id
date
description

目标是只在用户界面上还没有被占用的情况下,将action\types.description复制到actions.description。.

做了什么:

class ActionsController < ApplicationController
    active_scaffold :action do |c|
        c.columns = [ \
            , :date \
            , :action_type \
            , :description \
        ]
        c.columns[:action_type].form_ui = :select
        c.columns[:action_type].options[:update_column] = :description
        c.columns[:description].form_ui = :textarea
        c.columns[:description].options = { :cols => 40, :rows => 5}
    end

protected

    def after_render_field(record, column)
        # record: almost empty, only "action_type" is filled.
        # column: column.name == "action_type"
        # @params[]: id: id for the record
        # But no data on UI state. So if the user wrote some lines into the
        # description then it will be lost. No possibility
        # to express "do nothing!"
    end

    #...
end

另外,如果我们在“更新”期间仅在“创建”时没有此功能,我可以接受。这是一半,但现在就足够了。

有什么想法吗?

(Rails 2.3.4)