collection_start validates_presence_of冲突

Question

模型

class Task < ActiveRecord::Base
  attr_accessible :deadline, :list_id, :name, :summary
  validates_presence_of :deadline, :list_id, :name, :summary

  belongs_to :list
end

class List < ActiveRecord::Base
  attr_accessible :name

  has_many :tasks, :dependent => :destroy
end


<%= collection_select(:post, :list_id, List.all, :id, :name, :prompt => true) %>

渲染：

<select id="post_list_id" name="post[list_id]">
 <option value="">Please select</option>
 <option value="1">House</option>
 <option value="2">Car</option>
</select>

我将list_id设置为必需，当我在添加任务时从下拉列表中选择列表（list_id）时，它表示未选择list_id。我能做错什么？

更新：想通了，不得不修改表单视图中的collection_select行，我也没有包含f。部分到它

f.collection_select(:list_id, List.all, :id, :name, {:include_blank => true})