如何在 Ruby on Rails 3 中以嵌套形式调用对象的方法? [英] How to call a method on an object in a nested form in Ruby on Rails 3?

问题描述

我有这两个模型

class Invoice < ActiveRecord::Base
  has_many :items      
  accepts_nested_attributes_for :items
  ...
end

class Item < ActiveRecord::Base
  belongs_to :invoice

  def total
    price * quantity
  end
  ...
end

这个嵌套的 (!) 表单同时发布到两个模型:

and this nested (!) form that posts to both models:

<h1>Add an Invoice</h1>
<%= form_for @invoice do |f| %>
<p>
  <%= f.label :recipient %>
  <%= f.text_field :recipient %> </p>
<p>
  <%= f.label :date %>
  <%= f.text_area :date %>
</p>
<h2>Items</h2>
<p>
  <%= f.fields_for(:items) do |f| %>
    <%= f.label :description %>
    <%= f.text_field :description %>
    <%= f.label :price %>
    <%= f.text_field :price %>
    <%= f.label :quantity %>
    <%= f.text_field :quantity %>
    <%= f.label :total %>
    <%= f.total %><!-- this method call is not working! -->
  <% end %>
</p>
<%= f.submit %>
<% end %>

如何对表单中的项目进行计算?

How can I do calculations on my items within the form?

在我的 Items 模型中，我有这个方法:

In my Items model I have this method:

def total
  price * quantity
end

但是，在表单中我无法让它与 f.total 一起使用.我不断收到此错误:

However, in the form I can't get it to work with f.total. I keep getting this error:

undefined method `total' for #<ActionView::Helpers::FormBuilder:0x10ec05558>

我在这里遗漏了什么?

推荐答案

您不是在模型对象上调用方法，而是在 f 上调用方法，这是一个表单助手 (ActionView::Helpers::FormBuilder).错误消息对此给出了提示.

You are calling a method not on your model object, but on f, which is a form helper (ActionView::Helpers::FormBuilder). Error message gives a hint to this.

要调用该项目，您需要替换

To call on the item, you need to replace

<%= f.total %>

与

<%= f.object.total %>

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