轨道上的红宝石入门教程中的注释错误

我正在通过官方网站上的入门教程在轨道上学习Ruby。 http://guides.rubyonrails.org/getting_started.html

我唯一更改的是帖子网址映射指向/post/friendly-url 而不是/post/id

一切都很顺利，直到我尝试在帖子中添加评论，我收到以下错误。

NoMethodError in CommentsController#create

undefined method `comments' for nil:NilClass
app/controllers/comments_controller.rb:7:in `create'

这是我的代码。

app/controllers/comments_controller.rb

class CommentsController < ApplicationController
    def create
        @post = Post.find_by_friendly(params[:id])
        @comment = @post.comments.create(params[:comment])
        redirect_to post_path(@post)
    end
    def destroy
        @post = Post.find_by_friendly(params[:id])
        @comment = @post.comments.find(params[:id])
        @comment.destroy
        redirect_to post_path(@post)
    end
end

app/models/comment.rb

class Comment < ActiveRecord::Base
    belongs_to :post
    attr_accessible :body, :commenter
    validates :body,  :presence => true
    validates :commenter,  :presence => true
end

app/views/comments/_form.html.erb

<%= form_for([@post, @post.comments.build]) do |f| %>
<%= f.label :commenter, "Your Name:" %>
    <%= f.text_field :commenter, :placeholder => "Your Name..." %>
<span class="help-block">What would you like to be called.</span><br/>
<%= f.label :body, "Your Comment:" %>
    <%= f.text_area :body, :size => "60x12", :placeholder => "Your Comment..." %>
<span class="help-block">What's on your mind?</span><br/>
    <%= f.submit %>
<% end %>

app/views/posts/_form.html.erb

<% @post.tags.build %>
<%= form_for(@post) do |post_form| %>
<legend>Post Form</legend>
<% if @post.errors.any? %>
    <div id="error_explanation">
        <h2 class="text-error"><%= pluralize(@post.errors.count, "error") %> prohibited this post from being saved:</h2>
        <ul>
            <% @post.errors.full_messages.each do |msg| %>
                <li class="text-error"><%= msg %></li>
            <% end %>
        </ul>
    </div>
<% end %>
<%= post_form.label :name, "Post Name:" %>
    <%= post_form.text_field :name, :placeholder => "Post Name..." %>
<span class="help-block">The title of the article.</span><br/>
<%= post_form.label :friendly, "Friendly URL:" %>
    <%= post_form.text_field :friendly, :placeholder => "Friendly URL..." %>
<span class="help-block">SEO friendly URL displayed as /posts/post-name.</span><br/>
<%= post_form.label :content, "Post Content:" %>
<%= post_form.text_area :content, :size => "60x12", :placeholder => "Main Content..." %>
<span class="help-block">HTML enabled article content.</span><br/>
<%= post_form.label :excerpt, "Post Excerpt:" %>
    <%= post_form.text_area :excerpt, :placeholder => "Post Excerpt..." %>
<span class="help-block">Description of post for index page. No HTML.</span><br/>
<h2>Tags</h2>
<%= render :partial => 'tags/form',
    :locals => {:form => post_form} %><br/>
    <%= post_form.submit %>
<% end %>

config/routes.rb

Nullpulse::Application.routes.draw do
    resources :posts do
        resources :comments
    end
    root :to => "home#index"
end

apps/models/post.rb

class Post < ActiveRecord::Base
    attr_accessible :content, :friendly, :name, :excerpt, :tags_attributes
    validates :name,  :presence => true
    validates :content, :presence => true
    validates :friendly, :presence => true
    validates :excerpt, :presence => true
    validates_format_of :friendly, :with => /^[^ ]+$/
    has_many :comments, :dependent => :destroy
    has_many :tags
    accepts_nested_attributes_for :tags, :allow_destroy => :true,
        :reject_if => proc { |attrs| attrs.all? { |k, v| v.blank? } }
    def to_param
        friendly
    end
end

抱歉，如果信息太多，如果我遗漏了什么，也请告诉我。我一直在尝试一切，但找不到问题。提前谢谢。

问题是您在CommentController#create中的@post nil .这意味着，您提供的params[:id]不正确，或者数据库中找不到它。我建议检查日志以查看params[:id]包含的内容，并查看是否符合find_by_friendly的期望。

如果params[:id]看起来正确，我会使用 rails 控制台尝试Posts.find_by_friendly并传入一些值以查看是否适合您。

如果params[:id]值看起来不正确，那么您form_for()调用comments/_form.html.erb可能是错误的，请查看友好插件的文档以了解如何进行正确的调用。