Question

I am trying to show into article#index how many comments where on each articles.

So i have the following models

resources Article do
 resources Comments do
 end
end

I know in each article I can do the follow and this would work:

@count = @article.comments.find(:all).count

And just show in the view count. But then problem comes when i am in an index file and not sure how to show how many comments exist for this event atm.

Thanks in advance

Answer 1

articles_controller.rb

def index
  @articles = Article.all
end

articles/index.html.erb

<% @articles.each do |article| %>
  comments in article <%= article.comments.count %>
<% end %>

The nested routes (comments within articles) matters more in terms of your create/destroy routes for comments. Also be sure to add accepts_nested_attributes_for :comments in your Article model. This will allow you to do stuff like this:

for example, in articles_controller.rb

def show
  @article = Article.find(params[:id])

  # creates a new comment object with atricle_id already initialized
  @comment = @article.comments.build
end

Edit

If you do start caring about performance, I agree with Kitto’s comment.

Add this migration:

class AddCommentsCountToArtices < ActiveRecord::Migration
  def change
    add_column :articles, :comments_count, :integer, null: false, default: 0
  end
end

And change your relation declaration in your Comment model to this:

belongs_to :article, counter_cache: true

Then you can make calls like this article.comments_count to get the count instead of atricle.comments.count. And it’s great if the count is 0, because it doesn’t even make the query (p. 195 of The Rails 3 Way).

If you’re curious about how counter_cache works: it adds a callback to the belonging class (in this case, the Comment class) that updates the comments_counter attribute on the parent article each time a comment is created or destroyed.

Also, counter_cache functionality can easily be added to existing databases as demonstrated here, by Obie Fernandez.