Rails-NoMethodError-未定义的方法“名称”，为nil：NilClass

Question

我是Rails的新手，最近在从事学校项目时发现其中一个显示视图出错。 该错误与尚未定义名称方法有关，但我不确定如何解决此问题。 帮助将不胜感激！ 我收到的错误是：

NoMethodError in Topics#show

Showing /Users/Jason/code/bloccit/app/views/topics/show.html.erb where line #17 raised:

undefined method `name' for nil:NilClass

<%= link_to post.title, [@topic, post] %>
         </h4>
         <small>
           submitted <%= time_ago_in_words(post.created_at) %> ago by <%= post.user.name %><br>
           <%= post.comments.count %> Comments
         </small>
       </div>

相关文件包括..

topic / show.html.erb

<h1><%= @topic.name %></h1>

<% if policy(@topic).update? %>
  <%= link_to "Edit Topic", edit_topic_path, class: 'btn btn-success' %>
<% end %>

<div class="row">
  <div class="col-md-8">
    <p class="lead"><%= @topic.description %></p>
    <% @posts.each do |post| %>
      <div class="media">
        <div class="media-body">
          <h4 class="media-heading">
            <%= link_to post.title, [@topic, post] %>
          </h4>
          <small>
            submitted <%= time_ago_in_words(post.created_at) %> ago by <%= post.user.name %><br>
            <%= post.comments.count %> Comments
          </small>
        </div>
      </div>
    <% end %>
  </div>
  <div class="col-md-4">
    <% if policy(Post.new).create? %>
      <%= link_to "New Post", new_topic_post_path(@topic), class: 'btn btn-success' %>
    <% end %>
  </div>
</div>

post.rb

class Post < ActiveRecord::Base
  has_many :comments
  belongs_to :user
  belongs_to :topic

  default_scope { order('created_at DESC') }
end

topic.rb

class Topic < ActiveRecord::Base
  has_many :posts
end

posts_controller.rb

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

  def new
    @topic = Topic.find(params[:topic_id])
    @post = Post.new
    authorize @post
  end

  def create
    @topic = Topic.find(params[:topic_id])
    @post = Post.new(post_params)
    @post.topic = @topic
    authorize @post

    if @post.save
      flash[:notice] = "Post was saved."
      redirect_to [@topic, @post]
    else
      flash[:error] = "There was an error saving the post.  Please try again."
      render :new
    end
  end

  def edit
    @topic = Topic.find(params[:topic_id])
    @post = Post.find(params[:id])
    authorize @post
  end

  def update
    @topic = Topic.find(params[:topic_id])
    @post = Post.find(params[:id])
    authorize @post

    if @post.update_attributes(post_params)
      flash[:notice] = "Post was updated."
      redirect_to [@topic, @post]
    else
      flash[:error] = "There was an error saving the post.  Please try again."
      render :new
    end
  end

  private

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

topic_controller.rb

class TopicsController < ApplicationController
  def index
    @topics = Topic.all
    authorize @topics
  end

  def new
    @topic = Topic.new
    authorize @topic
  end

  def show
    @topic = Topic.find(params[:id])
    @posts = @topic.posts
    authorize @topic
  end

  def create
    @topic = Topic.new(topic_params)
    authorize @topic
    if @topic.save
      redirect_to @topic, notice: "Topic was saved successfully."
    else
      flash[:error] = "Error creating topic.  Please try again."
      render :new
    end
  end

  def edit
    @topic = Topic.find(params[:id])
    authorize @topic
  end

  def update
    @topic = Topic.find(params[:id])
    authorize @topic
    if @topic.update_attributes(topic_params)
      redirect_to @topic, notice: "Topic was updated successfully."
    else
      flash[:error] = "Error saving topic.  Please try again."
      render :edit
    end
  end

  private

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

Answer 1

您在创建帖子时未设置user ，我不确定您的authorize方法的实现。 然而，

它应该像

#assuming you have the user as `current_user`
class PostsController < ApplicationController
  ...
  def create
    @topic = Topic.find(params[:topic_id])
    @post = Post.new(post_params)
    @post.user = current_user
    @post.topic = @topic
    ...
  end 
  ...
end

Answer 2

您的帖子没有用户。 您必须检查为什么帖子没有保存用户。 为了防止出现此错误，您必须检查用户是否在帖子中。

我宁愿使用delegate并遵守得law of demeter的law of demeter

post.rb

class Post < ActiveRecord::Base
  has_many :comments
  belongs_to :user
  belongs_to :topic

  delegate :name, :to :user, allow_nil: true, prefix: true
  default_scope { order('created_at DESC') }
end

之后，您可以从帖子中接收用户名，例如post.user_name ，它将被转发到用户对象的name属性。

并更改您的show.html

<%= post.user.name %>

至

<%= post.user_name %>

其他：请不要使用default_scope。 如果您不需要order() ，则始终必须unscope查询。