Ruby on rails 使用的嵌套表单接受来自另一个表的预填充的嵌套属性

我使用的是Rails 2.3.5，其嵌套结构如下：

Lists has_many Items

Items_Features has_many Features
Items_Features has_many Items

Items_Features has a text field to hold the value of the feature

然后，我有一个嵌套表单，其中包含部分内容，以更新和显示该表单，从而更新列表、项目和项目功能

我想做的是为features中的每一行生成输入字段，以便用户可以填写一个值，并在features中插入/更新该值。我还希望框旁边有一个标签来显示要素名称

可能是这样的：

List name: Cheeses
    Item1 name: Edam
         Feature, hardness: - fill in - <= this list of features from feature table
         Feature, smell: - fill in -

当我把它发回时，试试这里的例子

---

嗨，威尔，谢谢你看这个。事实上，我已经大量使用了这个例子，非常好。不过，这并不能让我达到目的。我现在正在尝试使用find_by_sql来获取包含“cheesefeatures”空值的记录，如上所述。我将用sql编辑上面的文章，这样你就可以明白我的意思了。它正在显示我想要的功能。我只需要用一个隐藏的字段来保存item_功能，该字段可能是功能id？

class Item < ActiveRecord::Base
  belongs_to :list
  has_many :users
  has_many :votes
  has_many :items_features
  validates_presence_of :name, :message => "can't be blank"
  accepts_nested_attributes_for :items_features, :reject_if => lambda { |a| a.values.all?(&:blank?) }, :allow_destroy => true

  def self.get_two_random(list_id)
    Item.find_by_list_id(list_id, :limit => 2, :order => 'rand()')
  end

  def self.get_item_features(item_id)
    sql =  "select items_features.*, features.id as new_feature_id, features.name as feature_name "
    sql += "from items_features "
    sql += " right outer join features "
    sql += "  on features.id = items_features.feature_id "
    sql += " left outer join items "
    sql += "  on items.id = items_features.item_id "
    sql += "where items_features.item_id = ? or items_features.item_id is null"

    find_by_sql([sql, item_id])
  end

end

<% form_tag item_path, :method => :put do %>
 <% for items_feature in @item_features %>
  <% fields_for "items_features[]", items_feature do |f| %>
   <%=h items_feature.feature_name %> <%= f.text_field :featurevalue %><br><Br>
  <% end %>
 <% end %>
 <p><%= submit_tag "Submit"%></p>
<% end %>

/!\ FAILSAFE /!\  Thu Apr 15 16:44:59 +0100 2010
Status: 500 Internal Server Error
expected Array (got Hash) for param `items_features'