Ruby on rails 集合\u开始验证\u冲突的存在\u

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) %>

<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>

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