发布时显示Ruby on Rails错误

Question

我是RoR的初学者(8个小时),面临着一个我无法解决的问题.在其网站上的入门指南中提供的教程将通过设置帖子条目示例来完成.我收到以下错误:

NoMethodError in Posts#show
Showing /Users/khalidalghamdi/blog/app/views/posts/show.html.erb where line #3 raised:

undefined method `title' for nil:NilClass
Extracted source (around line #3):
1
2
3
4
5
6

  <p>
    <strong>Title:</strong>
    <%= @post.title %>
  </p>

  <p>

Rails.root: /Users/khalidalghamdi/blog

Application Trace | Framework Trace | Full Trace
app/views/posts/show.html.erb:3:in `_app_views_posts_show_html_erb__4427112910992919114_2164032300'
Request

Parameters:

{"id"=>"4"}

这是教程链接http://guides.rubyonrails.org/getting_started.html,我遵循5.6节.它没有在show.html.erb页面中显示已发布的详细信息.我究竟做错了什么？

更新:控制器代码:

class PostsController < ApplicationController
    def new

    end

    def create
        @post = Post.new(post_params)

        @post.save
        redirect_to @post
    end

    private
        def post_params
            params.require(:post).permit(:title, :text)
        end


    def show
        @post = Post.find(params[:id])
    end


end

Answer 1

设置实例变量@post的PostsController#show作用.目前,@post变量设置为nil,因此您将收到undefined method 'title' for nil:NilClass错误.

show从中删除操作private.它没有被调用,因为你已将其设为私有.因此@post没有设定.

例如:(由于您没有共享代码,我举一个例子)

class PostsController < ApplicationController
  ## ...
  def show
    @post = Post.find(params[:id])
  end
  ## ...

   private  
   def post_params
      params.require(:post).permit(:title, :text)
   end
end

此外,更好的方法是before_action在控制器中添加一个可以设置@post变量的方法,以避免多个操作之间的冗余代码.这也使你的代码DRY.

例如:

class PostsController < ApplicationController
  ## set_post would be called before show, edit, update and destroy action calls only
  before_action :set_post, only: [:show, :edit, :update, :destroy]
  ## ...

  def show
    ## No need to set @post here
  end

  ## ..
   private  

   def set_post
     @post = Post.find(params[:id])
   end

   def post_params
      params.require(:post).permit(:title, :text)
   end  
 end