Rails 3 - 未定义方法`model_name'为NilClass：当我尝试呈现'新'方法时的类

Question

我想在用户创建时保留表单中的值order（所以如果用户在字段中有错误，那么用户会得到页面与他/她已经打印的参数）。所以我接下来做

控制器

class OrdersController < ApplicationController 
    ... 

    def new 
    @everpresent_field_placeholder = "Fill that" 
    @order = Order.new 
    end 

    def create 
    order = Order.new(params[:order]) 

    if order.save 
     flash[:success] = "Yay! Order created!" 
    else 
     render 'new' 
     flash[:error] = order.errors.full_messages.to_sentence :last_word_connector => ", ",   
                  :two_words_connector => ", " 
    end 
    end 
end 

查看新秩序：

<legend>Order's creating</legend> 

<%= form_for @order, :html => {:class => "form-horizontal"} do |f| %> 
    <%= field_set_tag do %>  
    <div class="control-group"> 
     <%= f.label :number_of_order, "Number of order", :class => "control-label" %> 

     <div class="controls"> 
     <%= f.text_field :number_of_order, 
         :class => "span2",       
         :placeholder => @everpresent_field_placeholder %> 
     </div> 
    </div> 

    <%= f.submit "Create", :class => "btn btn-large btn-success" %> 
    <% end %> 
<% end %> 

但是，当我在订单的号码类型不对劲，然后单击“创建”我得到这样的错误：

NoMethodError in Orders#create 

Showing .../app/views/orders/new.html.erb where line #3 raised: 

undefined method `model_name' for NilClass:Class 

Extracted source (around line #3): 

1: <legend>Order's creating</legend> 
2: 
3: <%= form_for @order, :html => {:class => "form-horizontal"} do |f| %> 
4: <%= field_set_tag do %>  
5:  <div class="control-group"> 
6:  <%= f.label :number_of_order, "Number of order", :class => "control-label" %> 

我做错了什么？

Answer 1

调用render 'new'不会调用该控制器方法 - 它只会呈现与该操作关联的模板。也就是说，您的create操作从未设置@order - 也许如果您在create操作中替换对order和@order的引用，则会解决问题。