Ruby on Rails undefined 方法 'destroy' for nil：NilClass

Question

我在删除用户帖子时遇到问题：

未定义的方法nil：nilclass

# routes.rb
Rails.application.routes.draw do
  get 'sessions/new'
  get 'users/new'
  get 'user/new'
  root to:'pages#home'
  get '/home', to:'pages#home'
  get '/help', to:'pages#help'
  get '/about', to:'pages#about'
  get '/contact',  to:'pages#contact'
  get '/signup', to: 'users#new'
  post '/signup', to: 'users#create'
  get '/login', to: 'sessions#new'
  post '/login', to: 'sessions#create'
  delete '/logout', to: 'sessions#destroy'
  post '/micro_posts', to: 'microposts#create'
  delete '/micro_posts', to: 'microposts#destroy'
  resources :users
  resources :account_activations, only: [:edit]
  resources :microposts, only: [:create, :destroy]
end

# microposts_controller.rb 
class MicropostsController < ApplicationController
  before_action :logged_in_user, only: [:create, :destroy]
  before_action :correct_user, only: [:destroy]
  def create
    @micropost = current_user.micro_posts.build(req_params)
    if @micropost.save
        flash[:success] = "Post created"
        redirect_to root_url    
    else
        @feed_items = []
        render 'pages/home'
    end     
  end
  def destroy   
    @micropost.destroy
    flash[:success] = "Post deleted"
    redirect_to request.referrer || root_url
  end    
  private
  def req_params
    params.require(:micro_post).permit(:content)
  end
  def correct_user
    @micropost = current_user.micro_posts.find_by_id(params[:id])
    redirect_to root_url if @micropost.nil?
  end    
end
# _micro_post.html.erb file
<li id="micropost" ><%= micro_post.id %>
  <%= link_to gravatar_for(micro_post.user, size: 50), micro_post.user %>
  <span class="user" ><%= link_to micro_post.user.name, micro_post.user %></span><br/>
  <span class="content" ><%= micro_post.content %></span>
  <br/> 
  <span  class="timestamp">
  posted <%= time_ago_in_words(micro_post.created_at) %> ago    
  <% if current_user?(micro_post.user) %>
    <%= link_to '  | Delete', micro_posts_path, method: :delete , data: { confirm: "Are you sure" } %>
  <% end %>    
  </span>
  <br/>    
</li>

现在我想出的是我的错误是在microsts_controller.rb中参考方法中的文件"正确_user"，因为它找不到Micropost和返回零的ID。所以我们不能称呼销毁零对象上的方法。你能告诉我为什么不是吗查找Micropost ID？

Started DELETE "/micro_posts" for 127.0.0.1 at 2019-02-21 21:43:17 +0500
   (0.7ms)  SELECT "schema_migrations"."version" FROM "schema_migrations" ORDER BY "schema_migrations"."version" ASC
  ↳ C:/Ruby25-x64/lib/ruby/gems/2.5.0/gems/activerecord-5.2.2/lib/active_record/log_subscriber.rb:98
Processing by MicropostsController#destroy as HTML
  Parameters: {"authenticity_token"=>"aNeBnIy/JOrWz+sQdzU2w06faILW2dM+f8SPwmXVmJs1XfJ8OqbkgPVwkpoY/HBjh8YJhVPWZ4BC1Onxg0AtWw=="}
  User Load (0.2ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
  ↳ app/helpers/sessions_helper.rb:16
  MicroPost Load (0.3ms)  SELECT  "micro_posts".* FROM "micro_posts" WHERE "micro_posts"."id" IS NULL LIMIT ?  [["LIMIT", 1]]
  ↳ app/controllers/microposts_controller.rb:36
Completed 500 Internal Server Error in 56ms (ActiveRecord: 1.9ms)

NoMethodError (undefined method `destroy' for nil:NilClass):
app/controllers/microposts_controller.rb:22:in `destroy

Answer 1

它在您的correct_user方法中看起来有问题。尝试删除它并以这种方式使用：

class MicropostsController < ApplicationController
  before_action :logged_in_user, only: [:create, :destroy]
  before_action :set_micropost, only: :destroy
  ...
  def set_micropost
    @micropost ||= Micropost.find params[:id]
  end
end

和您的视图：

<%= link_to '  | Delete', @micropost, method: :delete , data: { confirm: "Are you sure" } %>

Answer 2

如果您不介意，我将把我的评论转换为答案，以免问题没有解决。

您有一个命名问题。该模型是MicroPost，但控制器是MicropostsController。这就是为什么您要创建自定义路线的原因。

您需要将控制器重命名为 MicroPostsController，并将其文件命名为 micro_posts_controller.rb。从路由中删除这2行：

post '/micro_posts', to: 'microposts#create'
delete '/micro_posts', to: 'microposts#destroy'

，然后将microposts更改为micro_posts（请注意下划线）：

resources :microposts, only: [:create, :destroy]

在视图中使用 micro_post_path(micro_post)进行删除链接

Answer 3

是的，您必须设置@micropost beofre的值，以销毁它。通常，这是您想要使用params哈希的事情，因此您可以在destroy方法开始时拥有像@micropost = Micropost.find(params[:id])这样的STH。这是您可能想在控制器中的其他方法中使用的行，因此您可以按以下方式进行重构

class MicropostsController < ApplicationController
  before_action :set_micropost, only: [:destroy]
 ...
  private
  def set_micropost
    @micropost = Micropost.find(params[:id])
  end
end

希望它有帮助：）

Answer 4

我认为您应该将ID参数传递到视图中的删除路由。

而不是这样：

<%= link_to ' | Delete', micro_posts_path, method: :delete , data: { confirm: "Are you sure" } %>

尝试以下操作： <%= link_to ' | Delete', micro_posts_path(micro_post.id), method: :delete , data: { confirm: "Are you sure" } %>

Answer 5

尝试以下：

<%= link_to '  | Delete', micro_post_path(micro_post), method: :delete , data: { confirm: "Are you sure" } %>

问题是您正在使用收集路线。micro_posts_path是一条集合路由，您需要使用获取资源ID的成员路由。因此，在这种情况下，我们从路线上删除s，并将其变成micro_post_path，即成员路由。

Answer 6

我没有注意到@zeitnot以相同的建议在我面前回答。

---

我认为您的问题是您的删除链接，而不是引用实际对象。您不是传递对象ID，因此params[:id]总是将是零。

尝试一下以查看它是否有效：

<% if current_user?(micro_post.user) %>
  <%= link_to '  | Delete', micro_post_path(micro_post), method: :delete , data: { confirm: "Are you sure" } %>
<% end %>