Question

I am working on building a blog with categorization. I am a bit stuck on how to implement categorization in the form. I have setup a has many through relationship and want to add check boxes to associate a blog with multiple categories. What I have so far is passing the categories through to the view, and I can list them out, however I cannot get the form_for method working for some reason.

Here is my code.

blog model

class Blog < ActiveRecord::Base
  attr_accessible :body, :title, :image
  has_many :categorizations
  has_many :categories, through: :categorizations
  has_attached_file :image, :styles => { :medium => "300x300>", :thumb => "100x100>" }

  validates :title, :body, :presence => true

end

Category Model

class Category < ActiveRecord::Base
  has_many :categorizations
  has_many :blogs, through: :categorizations
  attr_accessible :name
end

Categorization Model

class Categorization < ActiveRecord::Base
  attr_accessible :blog_id, :category_id
  belongs_to :blog
  belongs_to :category
end

Blog new controller

 def new
    @blog = Blog.new
    @categories = Category.all

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @blog }
    end
  end

Blog new form view

<%= form_for(@blog, :url => blogs_path, :html => { :multipart => true }) do |f| %>
  <% if @blog.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@blog.errors.count, "error") %> prohibited this blog from being saved:</h2>

      <ul>
      <% @blog.errors.full_messages.each do |msg| %>
        <li><%= msg %></li>
      <% end %>
      </ul>
    </div>
  <% end %>
   <div class="field">
    <%= f.label :title %><br />
    <%= f.text_field :title %>
  </div>
   <div class="field">
    <%= f.file_field :image %>
  </div>
  <div class="field">
    <%= f.label :body %><br />
    <%= f.text_area :body %>
  </div>
  <div class="field">
    Categories:
    <% @categories.each do |category| %>
      <% fields_for "blog[cat_attributes][]", category do |cat_form| %>
        <p>
          <%= cat_form.check_box :name %>
        </p>
      <% end %>
    <% end %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

This code is my failing point

<% @categories.each do |category| %>
          <% fields_for "blog[cat_attributes][]", category do |cat_form| %>
            <p>
              <%= cat_form.check_box :name %>
            </p>
          <% end %>
        <% end %>

Although I am not positive I am approaching any of it right since I am currently learning. Any advice on how to accomplish this.

Thanks,
CG

Answer 1

First of all, you probably don’t need a separate Categorization model unless there’s a use case you haven’t described here. You can set up a many-to-many relationship like this:

class Blog < ActiveRecord::Base
  has_and_belongs_to_many :categories
end

class Category < ActiveRecord::Base
  has_and_belongs_to_many :blogs
end

You should have a database table like this:

class CreateBlogsCategories < ActiveRecord::Migration
  def change
    create_table :blogs_categories, id: false do |t|
      t.references :blog
      t.references :category
    end
  end
end

Then you can construct the view like this:

<div class="field">
  Categories:
  <% @categories.each do |category| %>
    <%= label_tag do %>
      <%= check_box_tag 'blog[category_ids][]', category.id, @blog.category_ids.include?(category.id) %>
      <%= category.name %>
    <% end %>
  <% end %>
</div>

Lastly, in your form_for, you specify url: blogs_path – you should remove this if you plan to use this form for the edit action as well, because that should generate a PUT request to /blogs/:id. Assuming you used resources :blogs in routes.rb, Rails will determine the correct path for you based on the action used to render the form.