DIV class=FieldWitherRor去哪儿了?

我有以下简单的表格:

<% form_for(@weight) do |f| %>
  <%= f.error_messages %>
  <%= f.label :weight %>:
  <%= f.text_field :weight, :size => 5 %> kg.
  <%= f.submit "Add weight" %>
  <%= f.error_message_on :weight %>
<% end %>

它只显示一个字段的形式:权重。

通常呈现如下:

<form action="/weights" class="new_weight" id="new_weight" method="post">
  <div style="margin:0;padding:0;display:inline"><input name="authenticity_token" type="hidden" value="jYoVJkDnv4a1DMGnelJpGPElbH0XWKPNlESTt9GvzdA=" /></div>

  <label for="weight_weight">Weight</label>:
  <input id="weight_weight" name="weight[weight]" size="5" type="text" /> kg.
  <input id="weight_submit" name="commit" type="submit" value="Add weight" />
</form>

这很好。当我在不设置任何权重的情况下提交此表单时,会得到一个验证错误。f.error_messages和f.error_messages_on:weight正确显示错误消息,但是标签和文本字段没有像我通常在rails表单中预期的那样被类fieldwithorr包围在一个div中。我得到了这个:

<form action="/weights" class="new_weight" id="new_weight" method="post">
  <div style="margin:0;padding:0;display:inline"><input name="authenticity_token" type="hidden" value="jYoVJkDnv4a1DMGnelJpGPElbH0XWKPNlESTt9GvzdA=" /></div>

  <div class="errorExplanation" id="errorExplanation">
    <h2>1 error prohibited this weight from being saved</h2>
    <p>There were problems with the following fields:</p>
    <ul><li>Weight can't be blank</li></ul>
  </div>

  <label for="weight_weight">Weight</label>:
  <input id="weight_weight" name="weight[weight]" size="5" type="text" /> kg.
  <input id="weight_submit" name="commit" type="submit" value="Add weight" />

  <div class="formError">can't be blank</div>
</form>

作为参考,我应该得到的是:

<form action="/weights" class="new_weight" id="new_weight" method="post">
  <div style="margin:0;padding:0;display:inline"><input name="authenticity_token" type="hidden" value="jYoVJkDnv4a1DMGnelJpGPElbH0XWKPNlESTt9GvzdA=" /></div>

  <div class="errorExplanation" id="errorExplanation">
    <h2>1 error prohibited this weight from being saved</h2>
    <p>There were problems with the following fields:</p>
    <ul><li>Weight can't be blank</li></ul>
  </div>

  <div class="fieldWithErrors"><label for="weight_weight">Weight</label></div>:
  <div class="fieldWithErrors"><input id="weight_weight" name="weight[weight]" size="5" type="text" /></div> kg.
  <input id="weight_submit" name="commit" type="submit" value="Add weight" />
  <div class="formError">can't be blank</div>
</form>

你知道我为什么不买那些沙发吗?我安装了formtastic,它在其他形式中使用,但据我所知,它不应该干扰这个形式。

更新:只是为了确定,我打印了debug(@weight),它有错误:

--- &id002 !ruby/object:Weight 
attributes: 
  created_at: 
  updated_at: 

  weight: 
  measured_on: &id001 !timestamp 
    at: "2009-11-22 01:30:13.522589 +01:00"
    "@marshal_with_utc_coercion": false
  user_id: 1
attributes_cache: 
  measured_on: *id001
changed_attributes: 

  measured_on: 
  user_id: 
errors: !ruby/object:ActiveRecord::Errors 
  base: *id002
  errors: 
    weight: 
    - !ruby/object:ActiveRecord::Error 
      attribute: :weight

      base: *id002
      message: :blank
      options: {}

      type: :blank
new_record: true

更新:模型是

class Weight < ActiveRecord::Base
  belongs_to :user
  validates_presence_of :weight, :measured_on
  attr_accessible :weight, :measured_on

  def after_initialize
    self.measured_on ||= Time.now
  end

结束