未定义的方法`model_name＆＃39;对于＃<class：0xad3a8d8> </class：0xad3a8d8>

Question

我是编程的新手，我想知道如何在两个不同的视图中使用相同的代码，并且一个视图在浏览器中呈现而没有和错误，另一个视图在两个不同的视图中抛出错误浏览器。以下是<li><%= link_to "##{topic.name}", topic %></li>抛出的浏览器错误消息：

Showing /home/vagrant/code/bookmarks/app/views/user_bookmarks/index.html.erb where line #5 raised:

undefined method `model_name' for #<Class:0xad3a8d8>
Extracted source (around line #5):
  <ul class="topics">
      <% @topics.each do |topic| %>
        <li><%= link_to "##{topic.name}", topic %></li>
        <ul class="bookmarks">
          <%= render topic.bookmarks %>
        </ul>    

app/views/user_bookmarks/index.html.erb:5:in `block in _app_views_user_bookmarks_index_html_erb__225534477__624396848'
app/views/user_bookmarks/index.html.erb:4:in `each'
app/views/user_bookmarks/index.html.erb:4:in `_app_views_user_bookmarks_index_html_erb__225534477__624396848'

这是我的主题索引视图代码：

<h1>All Bookmarks</h1>

    <ul class="topics">
        <% @topics.each do |topic| %>
          <li><%= link_to "##{topic.name}", topic %></li>
          <ul class="bookmarks">
            <%= render topic.bookmarks %>
          </ul>    
        <% end %>
    </ul>
    <br>

这是我的用户书签索引视图代码的副本：

<h1>My Bookmarks</h1>

<ul class="topics">
    <% @topics.each do |topic| %>
      <li><%= link_to "##{topic.name}", topic %></li>
      <ul class="bookmarks">
        <%= render topic.bookmarks %>
      </ul>    
    <% end %>
</ul>
<br>

编辑：在此处添加控制器代码：

这是我的主题控制器：

class TopicsController < ApplicationController
  before_action :set_topic, only: [:show, :edit, :update, :destroy]

  def index
    @topics = Topic.all
  end

  def show
    @bookmarks = @topic.bookmarks
  end

  def new
    @topic = Topic.new
  end

  def edit
  end

  def create
    @topic = Topic.new(topic_params)

    respond_to do |format|
      if @topic.save
        format.html { redirect_to @topic, notice: 'Topic was successfully created.' }
        format.json { render action: 'show', status: :created, location: @topic }
      else
        format.html { render action: 'new' }
        format.json { render json: @topic.errors, status: :unprocessable_entity }
      end
    end
  end

  def update
    respond_to do |format|
      if @topic.update(topic_params)
        format.html { redirect_to @topic, notice: 'Topic was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @topic.errors, status: :unprocessable_entity }
      end
    end
  end

  def destroy
    @topic.destroy
    respond_to do |format|
      format.html { redirect_to topics_url }
      format.json { head :no_content }
    end
  end

  private
    def set_topic
      @topic = Topic.find(params[:id])
    end

    def topic_params
      params.require(:topic).permit(:name)
    end
end

这是我的书签控制器：

class BookmarksController < ApplicationController
  before_action :set_bookmark, only: [:show, :edit, :update, :destroy]

  def index
    @bookmarks = Bookmark.all
  end

  def show
  end

  def new
    @bookmark = Bookmark.new
  end

  def edit
  end

  def create
    bookmark = Bookmark.where(url: params[:bookmark][:url]).first

    @bookmark = bookmark.present? ? bookmark : Bookmark.new(bookmark_params)

    if @bookmark.save
      @bookmark.users << current_user
      Rails.logger.info ">>>>>>>>>>>>> Bookmark: #{@bookmark.inspect}"

      topic_names = params[:topic_names].split(' ')
      topic_names.each do |topic_name|
        name = topic_name.sub(/#/, '')

        @bookmark.topics << Topic.find_or_create_by_name(name)
      end
      respond_to do |format|
        format.html { redirect_to @bookmark, notice: 'Bookmark was successfully created.' }
        format.json { render action: 'show', status: :created, location: @bookmark }
      end
    else
      respond_to do |format|
        format.html { render action: 'new' }
        format.json { render json: @bookmark.errors, status: :unprocessable_entity }
      end
    end   
  end

  def update
    respond_to do |format|
      if @bookmark.update(bookmark_params)
        format.html { redirect_to @bookmark, notice: 'Bookmark was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @bookmark.errors, status: :unprocessable_entity }
      end
    end
  end

  def destroy
    @bookmark.destroy
    respond_to do |format|
      format.html { redirect_to bookmarks_url }
      format.json { head :no_content }
    end
  end

  private
    def set_bookmark
      @bookmark = Bookmark.find(params[:id])
    end

    def bookmark_params
      params.require(:bookmark).permit(:url)
    end
end

这是我的传入（书签和主题）控制器：

class BookmarksController < ApplicationController
  before_action :set_bookmark, only: [:show, :edit, :update, :destroy]

  def index
    @bookmarks = Bookmark.all
  end

  def show
  end

  def new
    @bookmark = Bookmark.new
  end

  def edit
  end

  def create
    bookmark = Bookmark.where(url: params[:bookmark][:url]).first

    @bookmark = bookmark.present? ? bookmark : Bookmark.new(bookmark_params)

    if @bookmark.save
      @bookmark.users << current_user
      Rails.logger.info ">>>>>>>>>>>>> Bookmark: #{@bookmark.inspect}"

      topic_names = params[:topic_names].split(' ')
      topic_names.each do |topic_name|
        name = topic_name.sub(/#/, '')

        @bookmark.topics << Topic.find_or_create_by_name(name)
      end
      respond_to do |format|
        format.html { redirect_to @bookmark, notice: 'Bookmark was successfully created.' }
        format.json { render action: 'show', status: :created, location: @bookmark }
      end
    else
      respond_to do |format|
        format.html { render action: 'new' }
        format.json { render json: @bookmark.errors, status: :unprocessable_entity }
      end
    end   
  end

  def update
    respond_to do |format|
      if @bookmark.update(bookmark_params)
        format.html { redirect_to @bookmark, notice: 'Bookmark was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: 'edit' }
        format.json { render json: @bookmark.errors, status: :unprocessable_entity }
      end
    end
  end

  def destroy
    @bookmark.destroy
    respond_to do |format|
      format.html { redirect_to bookmarks_url }
      format.json { head :no_content }
    end
  end

  private
    def set_bookmark
      @bookmark = Bookmark.find(params[:id])
    end

    def bookmark_params
      params.require(:bookmark).permit(:url)
    end
end

我的用户书签控制器：

class UserBookmarksController < ApplicationController
  def index
    @bookmarks = current_user.bookmarks
    #@topics = @bookmarks.collect(&:topics).uniq
    @liked_bookmarks = current_user.likes.collect(&:bookmark)
    @liked_topics = @liked_bookmarks.collect(&:topic).uniq
  end
end

如果你能帮助我理解为什么会这样，我真的很感激！谢谢！

Answer 1

您可能会因调用<%= link_to "text", topic %>

而导致错误

---

<强>对象

这是一个问题的原因是因为当您调用link_to helper时，需要使用路径填充它，以便Rails为您创建链接。虽然您的语法是正确的，但我相信您使用topic对象会引发错误。

有两种方法可以解决：

  

  
1. 更改您的link_to路径以直接引用路径助手
  
2. 修改您的topic对象以确保其正确
  

底线是当Rails使用＆＃34;帮助＆＃34;方法（其中link_to绝对是一个），它将依赖于对象中的大部分metadata来为您的系统提供功能。

model_name属性只是您的对象可以拥有的众多属性之一。我将看到的解决方案将解决缺少model_name：

的问题

---

链接

＆＃34;快速修复＆＃34;将直接在link_to中使用路径助手：

<%= link_to "##{topic.name}", topic_path(topic.id) %>

这只是语法改进，并认为您已正确定义topic_path路由：

#config/routes.rb
resources :topics #-> domain.com/topics/:id

这更像是一种外观变化 - 我相信真正的问题出现在你的对象声明中。

---

<强>声明

从topic调用您的@topics对象。从@topics操作调用TopicsController#index：

#app/controllers/topics_controller.rb
class TopicsController < ApplicationController
   def index
      @topics = Topic.all
   end
end

出于某种原因，这可能会导致Rails出现问题。我的直接想法是，您的Topic模型将无法正确设置，从而阻止Rails正确填充model_name属性

要解决此问题，我会确保您的Topic模型首先连接到您的数据库，其次是您修复任何关联。

Answer 2

我发现我收到了错误，因为没有直接的关系。改变这行代码：

@topics = @bookmarks.collect(&:topic).uniq

到这行代码工作：

@topics = @bookmarks.collect(&:topics).flatten.uniq

以下是我最终的工作代码在我的控制器中的样子：

class UserBookmarksController < ApplicationController
  def index
    @bookmarks = current_user.bookmarks
    @topics = @bookmarks.collect(&:topics).flatten.uniq
    @liked_bookmarks = current_user.likes.collect(&:bookmark)
    @liked_topics = @liked_bookmarks.collect(&:topic).uniq
  end
end