Having trouble rendering checkboxes in a Rails 4 many_to_many association - ruby-on-rails

Question

I have a many_to_many association between Categories and Articles, using has_and_belongs_to_many in a Rails 4 app:
Here are the corresponding migration and classes:
class CategoriesArticles < ActiveRecord::Migration
def change
create_table :categories_articles, id: false do |t|
t.belongs_to :category, index: true
t.belongs_to :article, index: true
end
add_index :categories_articles, [: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
When a user creates a new article, I simply want to give him or her the option to select categories that he/she wants to associate with the new article. I want the user to be able to select these categories with checkboxes.
Here's the 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 index
if user_signed_in?
#articles = current_user.article_feed
# TODO: if there are too few articles on a user's feed, we want to display more articles
else
#articles = Article.all
end
#articles = #articles.page(params[:page] || 1).per(12)
respond_with(#articles)
end
def show
respond_with(#article)
end
def new
#categories = Category.all
#article = Article.new
respond_with(#article)
end
def edit
if current_user.articles.find_by_id(params[:id]).nil?
flash[:notice] = "You do not have permission to edit this article."
redirect_to #article
end
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
def destroy
if #article
#article.destroy
flash[:notice] = "Article successfully destroyed."
else
flash[:notice] = "You do not have permission to delete this article."
end
# TODO: change this to another redirect location
redirect_to root_path
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
Here's the article new.html.erb view:
<h1>New article</h1>
<%= render 'form' %>
<%= link_to 'Back', articles_path %>
... and the form partial:
<%= 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 %>
However, this is erroring for me, specifically the lines:
<% #categories.each do |t| %>
<div class="field">
<%= f.label t.name %>
<%= f.check_box "categories[#{t.id}]" %>
<br />
</div>
<% end %>
Specifically, it's telling me:
undefined method 'categories[1]' for #<Article:0x007f401193d520>. How do I fix this? Thanks.

Answer 1

I note your join table is named
create_table :categories_articles, id: false do |t|
The name needs to be in alphabetical order.
create_table :articles_categories, id: false do |t|
My pick is that Rails cannot find your join table. This means that the form when it calls #article.categories cannot find what it needs. The same will happen if you call #category.articles (ie: being able to find the join table is not related to the arbitrary order of the objects).
See my answer to this question