How to obtain count of comments - ruby-on-rails

Question

This is my Articles index.html.erb so far
<table>
<tr>
<th>Title</th>
<th>Text</th>
<th colspan="3"></th>
<th>Total Number of Comments Per Article</th>
</tr>
<% #articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.text %></td>
<td><%= link_to 'Show', article_path(article) %></td>
<td><%= link_to 'Edit', edit_article_path(article) %></td>
<td><%= link_to 'Destroy', article_path(article),
method: :delete,
data: { confirm: 'Are you sure?' } %></td>
<td>Placeholder</td>
</tr>
<% end %>
</table>
<p>Total Number of Articles in database: <%= #count_of_articles %></p>
<h4>All Comments Written So Far</h>
<% #comments.each do |c| %>
<p><b><%= c.commenter %></b></p>
<p><%= c.body %></p>
<% end %>
<%= link_to 'New Article', new_article_path %>
This is my Article's index action
def index
#articles = Article.all
#count_of_articles = #articles.count
#comments = Comment.all
end
I am trying to figure out how to place the number of comments that each article has in the <td>Placeholder</td>
How do I do that?
EDIT
class Comment < ActiveRecord::Base
belongs_to :article
end
class Article < ActiveRecord::Base
has_many :comments, dependent: :destroy
validates :title, presence: true, length: { minimum: 5 }
end

Answer 1

by doing article.comments.count in the view you're basically running a sql query for each article in your db. Why not gather all records in your controller, and ask for the count in your view?, something like:
in the controller:
#comments_by_article = Comment.all.group_by(&:article_id)
and, in your view:
<td><%= #comments_by_article[article.id] && #comments_by_article[article.id].count || 0 %></td>
that way, rails will cache #comments_by_article in your controller, and you'll hitting the database once.

Answer 2

It is simply count:
<table>
<tr>
<th>Title</th>
<th>Text</th>
<th colspan="3"></th>
<th>Total Number of Comments Per Article</th>
</tr>
<% #articles.each do |article| %>
<tr>
<td><%= article.title %></td>
<td><%= article.text %></td>
<td><%= link_to 'Show', article_path(article) %></td>
<td><%= link_to 'Edit', edit_article_path(article) %></td>
<td><%= link_to 'Destroy', article_path(article),
method: :delete,
data: { confirm: 'Are you sure?' } %></td>
<td><%= article.comments.count %></td>
</tr>
<% end %>
</table>
article.comments is an ActiveRecord::Relation which extends the ActiveRecord::Calculations class containing the count method. The relation was defined in your model by you. Internally, ActiveRecord will call a COUNT SQL query to determine the number of comments that matches your article.

Answer 3

You can get the count with
article.comments.count