我试图做验证部分(http://guides.rubyonrails.org/getting_started.html#adding-some-validation),但是当我使用：

<% @post.errors.any? %>

我收到这个消息：

undefined method `errors' for nil:NilClass
Extracted source (around line #9):
<legend><h1>Add Post</h1></legend>
 
<%= form_for :post,url: posts_path,html: {class: 'form-horizontal'} do |f| %>
      <% if @post.errors.any? %>
        <div id="errorExplanation">

没有什么工作,我甚至复制和粘贴教程中的部分.

以下是该视图的代码：

<p> </p>
 
<div class="span6"
 
<fieldset>
    <legend><h1>Add Post</h1></legend>
 
    <%= form_for :post,html: {class: 'form-horizontal'} do |f| %>
          <% if @post.errors.any? %>
            <div id="errorExplanation">
 
                <h2><%= pluralize(@post.errors.count,"error") %> prohibited this post from being saved:</h2>
 
                <ul>
                    <% @post.errors.full_messages.each do |msg| %>
                    <li><%= msg %></li>
                    <% end %>
                  </ul>
            </div>
  <% end %>
        <div class="control-group">
            <%= f.label :title,:class => 'control-label' %>
            <div class="controls">
                <%= f.text_field :title,:class => 'span4' %>
            </div>
        </div>
 
        <div class="control-group">
            <%= f.label :content,:class => 'control-label' %>
            <div class="controls">
                <%= f.text_area :content,:rows => '7',:class => 'input-block-level' %>
            </div>
        </div>
 
        <div class="form-actions">
            <%= f.submit "Add Post",:class => 'btn btn-success' %>
            <%= link_to "Cancel",posts_path,:class => 'btn',:style => 'float:right;' %>
        </div>
    <% end %>
</fieldset>
 
</div>

和我的posts_controller：

class PostsController < ApplicationController
 
    def new
    end
 
    def create
        @post = Post.new(params[:post].permit(:title,:content))
 
        if @post.save
            redirect_to @post
        else
            render 'new'
        end
    end
 
    def show
        @post = Post.find(params[:id])
    end
 
    def index
        @posts = Post.order("created_at desc")
    end
 
    private
        def post_params
            params.require(:post).permit(:title,:content)
        end
 
end

我失踪了什么提前致谢！