访问嵌套形式部分变量时出现问题
我在 Rails 视图中有一个嵌套表单，像这样调用
<% f.fields_for :invoice_item_numbers do |item_no_form| %>
<%= render 'invoice_item_number', :f => item_no_form %>
<% end %>
，部分 (_invoice_item_number.html.erb) 看起来像这样
<div class='invoice_item_numbers'>
<% if f.object.new_record? %>
<li><%= f.label :item_number %><%= f.text_field :item_number %>
<%= link_to_function "remove", "$(this).parent().remove()", :class => 'remove_link' %></li>
<% else %>
<li class="inline"><%= f.label :item_number %><%= f.text_field :item_number %>
</li><li class="inline"><%= f.label :description %><%= invoice_item_number.description %></li><li><%= f.label :amount %><%= f.text_field :amount %>
<%= f.check_box '_destroy', :class => 'remove_checkbox' %>
<%= f.label '_destroy', 'remove', :class => 'remove_label' %></li>
<% end %>
</div>
这失败并显示错误消息
undefined method `description' for nil:NilClass
Why does unavailable_item_number return a nil object in thispart?它显然是以某种方式定义的，因为如果我将其更改为其他内容（例如 item_number.description ），则错误消息将变为 未定义的局部变量或方法item_number' for #相反，该部分显示的invoice_item_number对象被表单助手很好地使用为<%= f.text_field :item_number %>和<% f。 .text_field :amount %>两者都工作得很好。我尝试了多种解决方案，例如使用@invoice_item_number`并在渲染方法中显式定义对象，但这些
可能 都不起作用。对此有一个非常简单的答案。
I have a nested form in a rails view that is called like this
<% f.fields_for :invoice_item_numbers do |item_no_form| %>
<%= render 'invoice_item_number', :f => item_no_form %>
<% end %>
and the partial (_invoice_item_number.html.erb) looks like this
<div class='invoice_item_numbers'>
<% if f.object.new_record? %>
<li><%= f.label :item_number %><%= f.text_field :item_number %>
<%= link_to_function "remove", "$(this).parent().remove()", :class => 'remove_link' %></li>
<% else %>
<li class="inline"><%= f.label :item_number %><%= f.text_field :item_number %>
</li><li class="inline"><%= f.label :description %><%= invoice_item_number.description %></li><li><%= f.label :amount %><%= f.text_field :amount %>
<%= f.check_box '_destroy', :class => 'remove_checkbox' %>
<%= f.label '_destroy', 'remove', :class => 'remove_label' %></li>
<% end %>
</div>
This fails with the error message
undefined method `description' for nil:NilClass
Why does invoice_item_number return a nil object in this partial? It is obviously being defined somehow because if I change it to something else (e.g. item_number.description then the error message becomes undefined local variable or methoditem_number' for #instead. The invoice_item_number object that is being displayed by this partial is being used perfectly well by the form helpers as<%= f.text_field :item_number %>and<% f.text_field :amount %>both work perfectly well. I have tried a number of solutions such as using@invoice_item_number` and explicitly defining an object in the render method but these have not worked.
Presumably there is a very simple answer to this.
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只需重新阅读 Ryan 关于嵌套表单的剪贴帖，网址为 http://ryandaigle.com/articles/2009/2/1/what-s-new-in-edge-rails-nested-attributes并找到了答案。它已经在我的代码中了，但我不明白发生了什么。我可以使用 f.object 访问发票_item_number 对象，因此用
<%= f.object.description %>替换<%= Invoice_item_number.description %>解决了我的问题。Just re-read the Ryan's scraps post on nested forms at http://ryandaigle.com/articles/2009/2/1/what-s-new-in-edge-rails-nested-attributes and found the answer. It was sort of in my code already but I didn't understand what was happening. I can access the invoice_item_number object with f.object so replacing
<%= invoice_item_number.description %>with<%= f.object.description %>solved my problem.如何将： 更改
为
或如果您需要一个字段：
how about changing:
to
or if you need a field: