如何在list/index.html.erb上循环我的node.name

Question

在一个教程中，我知道一些类似的link_to代码。

lists/index.html.erb
<ul class="lists box">
<% lists.each do |list| %>
    <li>
        <h2 class="list_title">
            <%= link_to list.title, list %>
        </h2>
        <p>
          <%= truncate(list.content, length: 99) %>
          <br>
          <%= link_to list.node.name, list.node, class: "node" %>
        </p>
    </li>
<% end %>
</ul>

和2张表

  create_table "lists", force: :cascade do |t|
    t.string   "title"
    t.text     "content"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
    t.integer  "user_id"
    t.integer  "node_id"
  end
  create_table "nodes", force: :cascade do |t|
    t.string   "name"
    t.string   "summary"
    t.datetime "created_at", null: false
    t.datetime "updated_at", null: false
  end

2种型号

class Node < ActiveRecord::Base
    has_many :lists
end
class List < ActiveRecord::Base
    belongs_to :node 
end

控制器也可以

class ListsController < ApplicationController
  before_action :set_list, only: [:show, :edit, :update, :destroy]
  def index
    @lists = List.all.order(created_at: :desc).page(params[:page]).per(15)
  end
  def show
    @list = List.find(params[:id])
  end
.
.
.
  private
    def set_list
      @list = List.find(params[:id])
    end
    def list_params
      params.require(:list).permit(:title, :content)
    end
end

另一个控制器

class NodesController < ApplicationController
  before_action :set_node, only: [:show, :edit, :update, :destroy, :node_list]

  def index
    @nodes = Node.all
  end
  def show
    @node = Node.find(params[:id])
  end
.
.
.
.

我的路线

Rails.application.routes.draw do
  resources :lists, only: [:index, :show, :new]
  devise_for :users
  resources :users
  resources :nodes, only: [:show] 
  root 'lists#index'
end

当我跟踪s时，我得到了错误

NoMethodError in Lists#index
Showing /Users/zhangxiaodong/workspace/listlist/app/views/lists/_list_list.html.erb where line #10 raised:
undefined method `name' for nil:NilClass

当我将链接更改为<%= link_to list.node.name, list.node, class: "node" %>至<%= link_to "list.node.name", list.node, class: "node" %>页面没有错误，但node.name链接循环不在页面上。我查看API链接_to[http://api.rubyonrails.org/]，没有工作，你能告诉我如何循环我的节点吗。

Answer 1

lists/index.html.erb应该如下所示：

<ul class="lists box">
  <% lists.each do |list| %>
    <li>
      <h2 class="list_title">
        <%= link_to list.title, list_path(list) %>
      </h2>
      <p>
        <%= truncate(list.content, length: 99) %>
      <br>
        <%= link_to list.node.name, node_path(list.node), class: "node" if list.node.present? %>
     </p>
   </li>
 <% end %>
</ul>

Answer 2

因为您的list可能没有任何node。只需像这个一样修改代码

旧代码

<%= link_to list.node.name, list.node, class: "node" %>

新代码

<% if list.node %>
  <%= link_to list.node.name, list.node, class: "node" %>
<% end %>

Answer 3

尝试以下操作：

lists/index.html.erb

<ul class="lists box">
<% @lists.each do |list| %>
    <li>
        <h2 class="list_title">
            <%= link_to list.title, list_path(list) %>
        </h2>
        <p>
          <%= truncate(list.content, length: 99) %>
          <br>
          <%= link_to list.node.name, node_path(list.node), class: "node" %>
        </p>
    </li>
<% end %>
</ul>