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我有Articles和Categories之間的many_to_many協會，在Rails 4應用程序中使用has_and_belongs_to_many：無法渲染Rails 4 many_to_many關聯中的複選框？
這裏有相應的遷移和類：
class CategoriesArticles < ActiveRecord::Migration
def change
create_table :articles_categories, id: false do |t|
t.belongs_to :category, index: true
t.belongs_to :article, index: true
end
add_index :articles_categories, [:category_id, :article_id]
end
end
class Category < ActiveRecord::Base
has_and_belongs_to_many :articles
end
class Article < ActiveRecord::Base
has_and_belongs_to_many :categories
end
當用戶創建一個新的文章，我只是想給他或她選擇他/她想要與新文章相關聯的類別的選項。我希望用戶能夠用複選框選擇這些類別。
這裏的ArticlesController：
class ArticlesController < ApplicationController
before_action :set_article, only: [:show, :edit, :update, :destroy]
before_action :authenticate_user!, only: [:new, :create, :edit, :destroy, :update]
before_action :verify_own_article, only: [:destroy]
respond_to :html
...
def new
@categories = Category.all
@article = Article.new
respond_with(@article)
end
def create
# Creates article object with current_user_id, initial_comment, and URL
@article = current_user.articles.build(article_params)
# Uses Pismo (gem) to grab title, content, photo of URL
@article.populate_url_fields
if @article.save
flash[:success] = "Article created!"
# Might need to change the location of this redirect
redirect_to root_url
else
flash[:notice] = "Invalid article."
redirect_to new_article_path
end
end
def update
@article.update(article_params)
flash[:notice] = "Article successfully updated."
respond_with(@article)
end
private
def set_article
@article = Article.find(params[:id])
end
def article_params
params.require(:article).permit(:url, :title, :datetime, :content, :photo, :initial_comment)
end
# Ensure that a signed in user can only delete articles that they have posted
def verify_own_article
@article = current_user.articles.find_by_id(params[:id])
end
end
這裏的文章new.html.erb觀點：
<h1>New article</h1>
<%= render 'form' %>
<%= link_to 'Back', articles_path %>
...和form部分：
<%= form_for(@article) do |f| %>
<% if @article.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(@article.errors.count, "error") %> prohibited this article from being saved:</h2>
<ul>
<% @article.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :url %><br>
<%= f.text_field :url %>
</div>
<div class="field">
<%= f.label :initial_comment %><br>
<%= f.text_field :initial_comment %>
</div>
<% @categories.each do |t| %>
<div class="field">
<%= f.label t.name %>
<%= f.check_box "categories[#{t.id}]" %>
<br />
</div>
<% end %>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
然而，這示數爲我，特別是行：
<% @categories.each do |t| %>
<div class="field">
<%= f.label t.name %>
<%= f.check_box "categories[#{t.id}]" %>
<br />
</div>
<% end %>
具體來說，它告訴我：
undefined method 'categories[1]' for #<Article:0x007f401193d520>當我試圖渲染New Article頁面。我該如何解決？謝謝。